(#362) Part 4: handle unknown attributes by expanding type codes. r=nalexander

Also, don't run any SQL at all if an algebrized query is known to return no results.

core/src/lib.rs

@@ -74,11 +74,13 @@ impl TypedValue {
             &TypedValue::Keyword(_) => ValueType::Keyword,
         }
     }
+
 }
 
 // Put this here rather than in `db` simply because it's widely needed.
 pub trait SQLValueType {
     fn value_type_tag(&self) -> i32;
+    fn accommodates_integer(&self, int: i64) -> bool;
 }
 
 impl SQLValueType for ValueType {
@@ -94,6 +96,27 @@ impl SQLValueType for ValueType {
             ValueType::Keyword => 13,
         }
     }
+
+    /// Returns true if the provided integer is in the SQLite value space of this type. For
+    /// example, `1` is how we encode `true`.
+    ///
+    /// ```
+    /// use mentat_core::{ValueType, SQLValueType};
+    /// assert!(ValueType::Boolean.accommodates_integer(1));
+    /// assert!(!ValueType::Boolean.accommodates_integer(-1));
+    /// assert!(!ValueType::Boolean.accommodates_integer(10));
+    /// assert!(!ValueType::String.accommodates_integer(10));
+    /// ```
+    fn accommodates_integer(&self, int: i64) -> bool {
+        use ValueType::*;
+        match *self {
+            Instant | Long | Double => true,
+            Ref                     => int >= 0,
+            Boolean                 => (int == 0) || (int == 1),
+            ValueType::String       => false,
+            Keyword                 => false,
+        }
+    }
 }
 
 #[test]

query-algebrizer/src/cc.rs

@@ -134,23 +134,39 @@ pub fn default_table_aliaser() -> TableAliaser {
 
 #[derive(PartialEq, Eq)]
 pub enum ColumnConstraint {
+    EqualsColumn(QualifiedAlias, QualifiedAlias),
     EqualsEntity(QualifiedAlias, Entid),
     EqualsValue(QualifiedAlias, TypedValue),
-    EqualsColumn(QualifiedAlias, QualifiedAlias),
+
+    // This is different: a numeric value can only apply to the 'v' column, and it implicitly
+    // constrains the `value_type_tag` column. For instance, a primitive long on `datoms00` of `5`
+    // cannot be a boolean, so `datoms00.value_type_tag` must be in the set `#{0, 4, 5}`.
+    // Note that `5 = 5.0` in SQLite, and we preserve that here.
+    EqualsPrimitiveLong(TableAlias, i64),
+
+    HasType(TableAlias, ValueType),
 }
 
 impl Debug for ColumnConstraint {
     fn fmt(&self, f: &mut Formatter) -> Result {
         use self::ColumnConstraint::*;
         match self {
+            &EqualsColumn(ref qa1, ref qa2) => {
+                write!(f, "{:?} = {:?}", qa1, qa2)
+            }
             &EqualsEntity(ref qa, ref entid) => {
                 write!(f, "{:?} = entity({:?})", qa, entid)
             }
             &EqualsValue(ref qa, ref typed_value) => {
                 write!(f, "{:?} = value({:?})", qa, typed_value)
             }
-            &EqualsColumn(ref qa1, ref qa2) => {
+
-                write!(f, "{:?} = {:?}", qa1, qa2)
+            &EqualsPrimitiveLong(ref qa, value) => {
+                write!(f, "{:?}.v = primitive({:?})", qa, value)
+            }
+
+            &HasType(ref qa, value_type) => {
+                write!(f, "{:?}.value_type_tag = {:?}", qa, value_type)
             }
         }
     }
@@ -181,7 +197,7 @@ impl Debug for ColumnConstraint {
 ///---------------------------------------------------------------------------------------
 pub struct ConjoiningClauses {
     /// `true` if this set of clauses cannot yield results in the context of the current schema.
-    is_known_empty: bool,
+    pub is_known_empty: bool,
 
     /// A function used to generate an alias for a table -- e.g., from "datoms" to "datoms123".
     aliaser: TableAliaser,
@@ -264,6 +280,10 @@ impl ConjoiningClauses {
         self.constrain_column_to_entity(table, DatomsColumn::Attribute, attribute)
     }
 
+    pub fn constrain_value_to_numeric(&mut self, table: TableAlias, value: i64) {
+        self.wheres.push(ColumnConstraint::EqualsPrimitiveLong(table, value))
+    }
+
     /// Constrains the var if there's no existing type.
     /// Returns `false` if it's impossible for this type to apply (because there's a conflicting
     /// type already known).
@@ -601,7 +621,18 @@ impl ConjoiningClauses {
                 if let Some(ValueType::Ref) = value_type {
                     self.constrain_column_to_entity(col.clone(), DatomsColumn::Value, i);
                 } else {
-                    unimplemented!();
+                    // If we have a pattern like:
+                    //
+                    //   `[123 ?a 1]`
+                    //
+                    // then `1` could be an entid (ref), a long, a boolean, or an instant.
+                    //
+                    // We represent these constraints during execution:
+                    //
+                    // - Constraining the value column to the plain numeric value '1'.
+                    // - Constraining its type column to one of a set of types.
+                    //
+                    self.constrain_value_to_numeric(col.clone(), i);
                 },
             PatternValuePlace::IdentOrKeyword(ref kw) => {
                 // If we know the valueType, then we can determine whether this is an ident or a
@@ -637,7 +668,26 @@ impl ConjoiningClauses {
                 // TODO: if we don't know the type of the attribute because we don't know the
                 // attribute, we can actually work backwards to the set of appropriate attributes
                 // from the type of the value itself! #292.
+                let typed_value_type = typed_value.value_type();
                 self.constrain_column_to_constant(col.clone(), DatomsColumn::Value, typed_value);
+
+                // If we can't already determine the range of values in the DB from the attribute,
+                // then we must also constrain the type tag.
+                //
+                // Input values might be:
+                //
+                // - A long. This is handled by EntidOrInteger.
+                // - A boolean. This is unambiguous.
+                // - A double. This is currently unambiguous, though note that SQLite will equate 5.0 with 5.
+                // - A string. This is unambiguous.
+                // - A keyword. This is unambiguous.
+                //
+                // Because everything we handle here is unambiguous, we generate a single type
+                // restriction from the value type of the typed value.
+                if value_type.is_none() {
+                    self.wheres.push(ColumnConstraint::HasType(col.clone(), typed_value_type));
+                }
+
             },
         }
 
@@ -789,6 +839,7 @@ mod testing {
         // TODO: implement expand_type_tags.
         assert_eq!(cc.wheres, vec![
                    ColumnConstraint::EqualsValue(d0_v, TypedValue::Boolean(true)),
+                   ColumnConstraint::HasType("datoms00".to_string(), ValueType::Boolean),
         ]);
     }
 

query-algebrizer/src/lib.rs

@@ -34,6 +34,9 @@ pub struct AlgebraicQuery {
 }
 
 impl AlgebraicQuery {
+    /**
+     * Apply a new limit to this query, if one is provided and any existing limit is larger.
+     */
     pub fn apply_limit(&mut self, limit: Option<u64>) {
         match self.limit {
             None => self.limit = limit,
@@ -47,6 +50,10 @@ impl AlgebraicQuery {
                 },
         };
     }
+
+    pub fn is_known_empty(&self) -> bool {
+        self.cc.is_known_empty
+    }
 }
 
 #[allow(dead_code)]

query-projector/src/lib.rs

@@ -100,6 +100,36 @@ impl QueryResults {
             &Rel(ref v)    => v.len(),
         }
     }
+
+    pub fn is_empty(&self) -> bool {
+        use QueryResults::*;
+        match self {
+            &Scalar(ref o) => o.is_none(),
+            &Tuple(ref o)  => o.is_none(),
+            &Coll(ref v)   => v.is_empty(),
+            &Rel(ref v)    => v.is_empty(),
+        }
+    }
+
+    pub fn empty(spec: &FindSpec) -> QueryResults {
+        use self::FindSpec::*;
+        match spec {
+            &FindScalar(_) => QueryResults::Scalar(None),
+            &FindTuple(_)  => QueryResults::Tuple(None),
+            &FindColl(_)   => QueryResults::Coll(vec![]),
+            &FindRel(_)    => QueryResults::Rel(vec![]),
+        }
+    }
+
+    pub fn empty_factory(spec: &FindSpec) -> Box<Fn() -> QueryResults> {
+        use self::FindSpec::*;
+        match spec {
+            &FindScalar(_) => Box::new(|| QueryResults::Scalar(None)),
+            &FindTuple(_)  => Box::new(|| QueryResults::Tuple(None)),
+            &FindColl(_)   => Box::new(|| QueryResults::Coll(vec![])),
+            &FindRel(_)    => Box::new(|| QueryResults::Rel(vec![])),
+        }
+    }
 }
 
 type Index = i32;            // See rusqlite::RowIndex.
@@ -216,6 +246,24 @@ pub trait Projector {
     fn project<'stmt>(&self, rows: Rows<'stmt>) -> Result<QueryResults>;
 }
 
+/// A projector that produces a `QueryResult` containing fixed data.
+/// Takes a boxed function that should return an empty result set of the desired type.
+struct ConstantProjector {
+    results_factory: Box<Fn() -> QueryResults>,
+}
+
+impl ConstantProjector {
+    fn new(results_factory: Box<Fn() -> QueryResults>) -> ConstantProjector {
+        ConstantProjector { results_factory: results_factory }
+    }
+}
+
+impl Projector for ConstantProjector {
+    fn project<'stmt>(&self, _: Rows<'stmt>) -> Result<QueryResults> {
+        Ok((self.results_factory)())
+    }
+}
+
 struct ScalarProjector {
     template: TypedIndex,
 }
@@ -396,28 +444,39 @@ pub struct CombinedProjection {
 pub fn query_projection(query: &AlgebraicQuery) -> CombinedProjection {
     use self::FindSpec::*;
 
-    match query.find_spec {
+    if query.is_known_empty() {
-        FindColl(ref element) => {
+        // Do a few gyrations to produce empty results of the right kind for the query.
-            let (cols, templates) = project_elements(1, iter::once(element), query);
+        let empty = QueryResults::empty_factory(&query.find_spec);
-            CollProjector::combine(cols, templates)
+        let constant_projector = ConstantProjector::new(empty);
-        },
+        CombinedProjection {
+            sql_projection: Projection::One,
 
-        FindScalar(ref element) => {
+            datalog_projector: Box::new(constant_projector),
-            let (cols, templates) = project_elements(1, iter::once(element), query);
+        }
-            ScalarProjector::combine(cols, templates)
+    } else {
-        },
+        match query.find_spec {
+            FindColl(ref element) => {
+                let (cols, templates) = project_elements(1, iter::once(element), query);
+                CollProjector::combine(cols, templates)
+            },
 
-        FindRel(ref elements) => {
+            FindScalar(ref element) => {
-            let column_count = query.find_spec.expected_column_count();
+                let (cols, templates) = project_elements(1, iter::once(element), query);
-            let (cols, templates) = project_elements(column_count, elements, query);
+                ScalarProjector::combine(cols, templates)
-            RelProjector::combine(column_count, cols, templates)
+            },
-        },
 
-        FindTuple(ref elements) => {
+            FindRel(ref elements) => {
-            let column_count = query.find_spec.expected_column_count();
+                let column_count = query.find_spec.expected_column_count();
-            let (cols, templates) = project_elements(column_count, elements, query);
+                let (cols, templates) = project_elements(column_count, elements, query);
-            TupleProjector::combine(column_count, cols, templates)
+                RelProjector::combine(column_count, cols, templates)
-        },
+            },
+
+            FindTuple(ref elements) => {
+                let column_count = query.find_spec.expected_column_count();
+                let (cols, templates) = project_elements(column_count, elements, query);
+                TupleProjector::combine(column_count, cols, templates)
+            },
+        }
     }
 }
 

query-sql/src/lib.rs

@@ -44,6 +44,7 @@ use mentat_sql::{
 pub enum ColumnOrExpression {
     Column(QualifiedAlias),
     Entid(Entid),       // Because it's so common.
+    Integer(i32),       // We use these for type codes etc.
     Value(TypedValue),
 }
 
@@ -64,11 +65,26 @@ pub enum Constraint {
     Infix {
         op: Op,
         left: ColumnOrExpression,
-        right: ColumnOrExpression
+        right: ColumnOrExpression,
+    },
+    And {
+        constraints: Vec<Constraint>,
+    },
+    In {
+        left: ColumnOrExpression,
+        list: Vec<ColumnOrExpression>,
     }
 }
 
 impl Constraint {
+    pub fn not_equal(left: ColumnOrExpression, right: ColumnOrExpression) -> Constraint {
+        Constraint::Infix {
+            op: Op("<>"),     // ANSI SQL for future-proofing!
+            left: left,
+            right: right,
+        }
+    }
+
     pub fn equal(left: ColumnOrExpression, right: ColumnOrExpression) -> Constraint {
         Constraint::Infix {
             op: Op("="),
@@ -86,6 +102,12 @@ enum JoinOp {
 // Short-hand for a list of tables all inner-joined.
 pub struct TableList(pub Vec<SourceAlias>);
 
+impl TableList {
+    fn is_empty(&self) -> bool {
+        self.0.is_empty()
+    }
+}
+
 pub struct Join {
     left: TableOrSubquery,
     op: JoinOp,
@@ -102,6 +124,7 @@ enum TableOrSubquery {
 pub enum FromClause {
     TableList(TableList),      // Short-hand for a pile of inner joins.
     Join(Join),
+    Nothing,
 }
 
 pub struct SelectQuery {
@@ -119,6 +142,35 @@ fn push_column(qb: &mut QueryBuilder, col: &DatomsColumn) {
 //---------------------------------------------------------
 // Turn that representation into SQL.
 
+
+/// A helper macro to sequentially process an iterable sequence,
+/// evaluating a block between each pair of items.
+///
+/// This is used to simply and efficiently produce output like
+///
+/// ```sql
+///   1, 2, 3
+/// ```
+///
+/// or
+///
+/// ```sql
+/// x = 1 AND y = 2
+/// ```
+///
+/// without producing an intermediate string sequence.
+macro_rules! interpose {
+    ( $name: ident, $across: expr, $body: block, $inter: block ) => {
+        let mut seq = $across.iter();
+        if let Some($name) = seq.next() {
+            $body;
+            for $name in seq {
+                $inter;
+                $body;
+            }
+        }
+    }
+}
 impl QueryFragment for ColumnOrExpression {
     fn push_sql(&self, out: &mut QueryBuilder) -> BuildQueryResult {
         use self::ColumnOrExpression::*;
@@ -133,6 +185,10 @@ impl QueryFragment for ColumnOrExpression {
                 out.push_sql(entid.to_string().as_str());
                 Ok(())
             },
+            &Integer(integer) => {
+                out.push_sql(integer.to_string().as_str());
+                Ok(())
+            },
             &Value(ref v) => {
                 out.push_typed_value(v)
             },
@@ -172,19 +228,6 @@ impl QueryFragment for Op {
     }
 }
 
-macro_rules! interpose {
-    ( $name: ident, $across: expr, $body: block, $inter: block ) => {
-        let mut seq = $across.iter();
-        if let Some($name) = seq.next() {
-            $body;
-            for $name in seq {
-                $inter;
-                $body;
-            }
-        }
-    }
-}
-
 impl QueryFragment for Constraint {
     fn push_sql(&self, out: &mut QueryBuilder) -> BuildQueryResult {
         use self::Constraint::*;
@@ -195,7 +238,26 @@ impl QueryFragment for Constraint {
                 op.push_sql(out)?;
                 out.push_sql(" ");
                 right.push_sql(out)
-            }
+            },
+
+            &And { ref constraints } => {
+                out.push_sql("(");
+                interpose!(constraint, constraints,
+                           { constraint.push_sql(out)? },
+                           { out.push_sql(" AND ") });
+                out.push_sql(")");
+                Ok(())
+            },
+
+            &In { ref left, ref list } => {
+                left.push_sql(out)?;
+                out.push_sql(" IN (");
+                interpose!(item, list,
+                           { item.push_sql(out)? },
+                           { out.push_sql(", ") });
+                out.push_sql(")");
+                Ok(())
+            },
         }
     }
 }
@@ -249,8 +311,19 @@ impl QueryFragment for FromClause {
     fn push_sql(&self, out: &mut QueryBuilder) -> BuildQueryResult {
         use self::FromClause::*;
         match self {
-            &TableList(ref table_list) => table_list.push_sql(out),
+            &TableList(ref table_list) => {
-            &Join(ref join) => join.push_sql(out),
+                if table_list.is_empty() {
+                    Ok(())
+                } else {
+                    out.push_sql(" FROM ");
+                    table_list.push_sql(out)
+                }
+            },
+            &Join(ref join) => {
+                out.push_sql(" FROM ");
+                join.push_sql(out)
+            },
+            &Nothing => Ok(()),
         }
     }
 }
@@ -259,19 +332,15 @@ impl QueryFragment for SelectQuery {
     fn push_sql(&self, out: &mut QueryBuilder) -> BuildQueryResult {
         out.push_sql("SELECT ");
         self.projection.push_sql(out)?;
-
-        out.push_sql(" FROM ");
         self.from.push_sql(out)?;
 
-        if self.constraints.is_empty() {
+        if !self.constraints.is_empty() {
-            return Ok(());
+            out.push_sql(" WHERE ");
+            interpose!(constraint, self.constraints,
+                       { constraint.push_sql(out)? },
+                       { out.push_sql(" AND ") });
         }
 
-        out.push_sql(" WHERE ");
-        interpose!(constraint, self.constraints,
-                   { constraint.push_sql(out)? },
-                   { out.push_sql(" AND ") });
-
         // Guaranteed to be positive: u64.
         if let Some(limit) = self.limit {
             out.push_sql(" LIMIT ");
@@ -294,6 +363,67 @@ mod tests {
     use super::*;
     use mentat_query_algebrizer::DatomsTable;
 
+    fn build_constraint(c: Constraint) -> String {
+        let mut builder = SQLiteQueryBuilder::new();
+        c.push_sql(&mut builder)
+         .map(|_| builder.finish())
+         .unwrap().sql
+    }
+
+    #[test]
+    fn test_in_constraint() {
+        let none = Constraint::In {
+            left: ColumnOrExpression::Column(QualifiedAlias("datoms01".to_string(), DatomsColumn::Value)),
+            list: vec![],
+        };
+
+        let one = Constraint::In {
+            left: ColumnOrExpression::Column(QualifiedAlias("datoms01".to_string(), DatomsColumn::Value)),
+            list: vec![
+                ColumnOrExpression::Entid(123),
+            ],
+        };
+
+        let three = Constraint::In {
+            left: ColumnOrExpression::Column(QualifiedAlias("datoms01".to_string(), DatomsColumn::Value)),
+            list: vec![
+                ColumnOrExpression::Entid(123),
+                ColumnOrExpression::Entid(456),
+                ColumnOrExpression::Entid(789),
+            ],
+        };
+
+        assert_eq!("`datoms01`.v IN ()", build_constraint(none));
+        assert_eq!("`datoms01`.v IN (123)", build_constraint(one));
+        assert_eq!("`datoms01`.v IN (123, 456, 789)", build_constraint(three));
+    }
+
+    #[test]
+    fn test_and_constraint() {
+        let c = Constraint::And {
+            constraints: vec![
+                Constraint::And {
+                    constraints: vec![
+                        Constraint::Infix {
+                            op: Op("="),
+                            left: ColumnOrExpression::Entid(123),
+                            right: ColumnOrExpression::Entid(456),
+                        },
+                        Constraint::Infix {
+                            op: Op("="),
+                            left: ColumnOrExpression::Entid(789),
+                            right: ColumnOrExpression::Entid(246),
+                        },
+                    ],
+                },
+            ],
+        };
+
+        // Two sets of parens: the outermost AND only has one child,
+        // but still contributes parens.
+        assert_eq!("((123 = 456 AND 789 = 246))", build_constraint(c));
+    }
+
     #[test]
     fn test_end_to_end() {
 

query-translator/src/lib.rs

@@ -23,6 +23,5 @@ pub use mentat_query_sql::{
 
 pub use translate::{
     cc_to_exists,
-    cc_to_select,
     query_to_select,
 };

query-translator/src/translate.rs

@@ -10,6 +10,12 @@
 
 #![allow(dead_code, unused_imports)]
 
+use mentat_core::{
+    SQLValueType,
+    TypedValue,
+    ValueType,
+};
+
 use mentat_query::{
     Element,
     FindSpec,
@@ -64,45 +70,106 @@ impl ToConstraint for ColumnConstraint {
         match self {
             EqualsEntity(qa, entid) =>
                 Constraint::equal(qa.to_column(), ColumnOrExpression::Entid(entid)),
+
             EqualsValue(qa, tv) =>
                 Constraint::equal(qa.to_column(), ColumnOrExpression::Value(tv)),
+
             EqualsColumn(left, right) =>
                 Constraint::equal(left.to_column(), right.to_column()),
+
+            EqualsPrimitiveLong(table, value) => {
+                let value_column = QualifiedAlias(table.clone(), DatomsColumn::Value).to_column();
+                let tag_column = QualifiedAlias(table, DatomsColumn::ValueTypeTag).to_column();
+
+                /// A bare long in a query might match a ref, an instant, a long (obviously), or a
+                /// double. If it's negative, it can't match a ref, but that's OK -- it won't!
+                ///
+                /// However, '1' and '0' are used to represent booleans, and some integers are also
+                /// used to represent FTS values. We don't want to accidentally match those.
+                ///
+                /// We ask `SQLValueType` whether this value is in range for how booleans are
+                /// represented in the database.
+                ///
+                /// We only hit this code path when the attribute is unknown, so we're querying
+                /// `all_datoms`. That means we don't see FTS IDs at all -- they're transparently
+                /// replaced by their strings. If that changes, then you should also exclude the
+                /// string type code (10) here.
+                let must_exclude_boolean = ValueType::Boolean.accommodates_integer(value);
+                if must_exclude_boolean {
+                    Constraint::And {
+                        constraints: vec![
+                            Constraint::equal(value_column,
+                                              ColumnOrExpression::Value(TypedValue::Long(value))),
+                            Constraint::not_equal(tag_column,
+                                                  ColumnOrExpression::Integer(ValueType::Boolean.value_type_tag())),
+                        ],
+                    }
+                } else {
+                    Constraint::equal(value_column, ColumnOrExpression::Value(TypedValue::Long(value)))
+                }
+            },
+
+            HasType(table, value_type) => {
+                let column = QualifiedAlias(table, DatomsColumn::ValueTypeTag).to_column();
+                Constraint::equal(column, ColumnOrExpression::Integer(value_type.value_type_tag()))
+            },
         }
     }
 }
 
-pub struct CombinedSelectQuery {
+pub struct ProjectedSelect{
     pub query: SelectQuery,
     pub projector: Box<Projector>,
 }
 
+/// Returns a `SelectQuery` that queries for the provided `cc`. Note that this _always_ returns a
+/// query that runs SQL. The next level up the call stack can check for known-empty queries if
+/// needed.
 fn cc_to_select_query<T: Into<Option<u64>>>(projection: Projection, cc: ConjoiningClauses, limit: T) -> SelectQuery {
+    let from = if cc.from.is_empty() {
+        FromClause::Nothing
+    } else {
+        FromClause::TableList(TableList(cc.from))
+    };
     SelectQuery {
         projection: projection,
-        from: FromClause::TableList(TableList(cc.from)),
+        from: from,
         constraints: cc.wheres
                        .into_iter()
                        .map(|c| c.to_constraint())
                        .collect(),
-        limit: limit.into(),
+        limit: if cc.is_known_empty { Some(0) } else { limit.into() },
+    }
+}
+
+/// Return a query that projects `1` if the `cc` matches the store, and returns no results
+/// if it doesn't.
+pub fn cc_to_exists(cc: ConjoiningClauses) -> SelectQuery {
+    if cc.is_known_empty {
+        // In this case we can produce a very simple query that returns no results.
+        SelectQuery {
+            projection: Projection::One,
+            from: FromClause::Nothing,
+            constraints: vec![],
+            limit: Some(0),
+        }
+    } else {
+        cc_to_select_query(Projection::One, cc, 1)
     }
 }
 
 /// Consume a provided `ConjoiningClauses` to yield a new
-/// `SelectQuery`. A projection list must also be provided.
+/// `ProjectedSelect`. A projection list must also be provided.
-pub fn cc_to_select(projection: CombinedProjection, cc: ConjoiningClauses, limit: Option<u64>) -> CombinedSelectQuery {
+fn cc_to_select(projection: CombinedProjection, cc: ConjoiningClauses, limit: Option<u64>) -> ProjectedSelect {
     let CombinedProjection { sql_projection, datalog_projector } = projection;
-    CombinedSelectQuery {
+    ProjectedSelect {
         query: cc_to_select_query(sql_projection, cc, limit),
         projector: datalog_projector,
     }
 }
 
-pub fn query_to_select(query: AlgebraicQuery) -> CombinedSelectQuery {
+/// Consume a provided `AlgebraicQuery` to yield a new
+/// `ProjectedSelect`.
+pub fn query_to_select(query: AlgebraicQuery) -> ProjectedSelect {
     cc_to_select(query_projection(&query), query.cc, query.limit)
 }
-
-pub fn cc_to_exists(cc: ConjoiningClauses) -> SelectQuery {
-    cc_to_select_query(Projection::One, cc, 1)
-}

query-translator/tests/translate.rs

@@ -41,6 +41,14 @@ fn add_attribute(schema: &mut Schema, e: Entid, a: Attribute) {
     schema.schema_map.insert(e, a);
 }
 
+fn translate<T: Into<Option<u64>>>(schema: &Schema, input: &'static str, limit: T) -> SQLQuery {
+    let parsed = parse_find_string(input).expect("parse failed");
+    let mut algebrized = algebrize(schema, parsed);
+    algebrized.apply_limit(limit.into());
+    let select = query_to_select(algebrized);
+    select.query.to_sql_query().unwrap()
+}
+
 #[test]
 fn test_coll() {
     let mut schema = Schema::default();
@@ -51,10 +59,7 @@ fn test_coll() {
     });
 
     let input = r#"[:find [?x ...] :where [?x :foo/bar "yyy"]]"#;
-    let parsed = parse_find_string(input).expect("parse failed");
+    let SQLQuery { sql, args } = translate(&schema, input, None);
-    let algebrized = algebrize(&schema, parsed);
-    let select = query_to_select(algebrized);
-    let SQLQuery { sql, args } = select.query.to_sql_query().unwrap();
     assert_eq!(sql, "SELECT `datoms00`.e AS `?x` FROM `datoms` AS `datoms00` WHERE `datoms00`.a = 99 AND `datoms00`.v = $v0");
     assert_eq!(args, vec![("$v0".to_string(), "yyy".to_string())]);
 }
@@ -69,10 +74,7 @@ fn test_rel() {
     });
 
     let input = r#"[:find ?x :where [?x :foo/bar "yyy"]]"#;
-    let parsed = parse_find_string(input).expect("parse failed");
+    let SQLQuery { sql, args } = translate(&schema, input, None);
-    let algebrized = algebrize(&schema, parsed);
-    let select = query_to_select(algebrized);
-    let SQLQuery { sql, args } = select.query.to_sql_query().unwrap();
     assert_eq!(sql, "SELECT `datoms00`.e AS `?x` FROM `datoms` AS `datoms00` WHERE `datoms00`.a = 99 AND `datoms00`.v = $v0");
     assert_eq!(args, vec![("$v0".to_string(), "yyy".to_string())]);
 }
@@ -87,11 +89,92 @@ fn test_limit() {
     });
 
     let input = r#"[:find ?x :where [?x :foo/bar "yyy"]]"#;
-    let parsed = parse_find_string(input).expect("parse failed");
+    let SQLQuery { sql, args } = translate(&schema, input, 5);
-    let mut algebrized = algebrize(&schema, parsed);
-    algebrized.limit = Some(5);
-    let select = query_to_select(algebrized);
-    let SQLQuery { sql, args } = select.query.to_sql_query().unwrap();
     assert_eq!(sql, "SELECT `datoms00`.e AS `?x` FROM `datoms` AS `datoms00` WHERE `datoms00`.a = 99 AND `datoms00`.v = $v0 LIMIT 5");
     assert_eq!(args, vec![("$v0".to_string(), "yyy".to_string())]);
 }
+
+#[test]
+fn test_unknown_attribute_keyword_value() {
+    let schema = Schema::default();
+
+    let input = r#"[:find ?x :where [?x _ :ab/yyy]]"#;
+    let SQLQuery { sql, args } = translate(&schema, input, None);
+
+    // Only match keywords, not strings: tag = 13.
+    assert_eq!(sql, "SELECT `datoms00`.e AS `?x` FROM `datoms` AS `datoms00` WHERE `datoms00`.v = $v0 AND `datoms00`.value_type_tag = 13");
+    assert_eq!(args, vec![("$v0".to_string(), ":ab/yyy".to_string())]);
+}
+
+#[test]
+fn test_unknown_attribute_string_value() {
+    let schema = Schema::default();
+
+    let input = r#"[:find ?x :where [?x _ "horses"]]"#;
+    let SQLQuery { sql, args } = translate(&schema, input, None);
+
+    // We expect all_datoms because we're querying for a string. Magic, that.
+    // We don't want keywords etc., so tag = 10.
+    assert_eq!(sql, "SELECT `all_datoms00`.e AS `?x` FROM `all_datoms` AS `all_datoms00` WHERE `all_datoms00`.v = $v0 AND `all_datoms00`.value_type_tag = 10");
+    assert_eq!(args, vec![("$v0".to_string(), "horses".to_string())]);
+}
+
+#[test]
+fn test_unknown_attribute_double_value() {
+    let schema = Schema::default();
+
+    let input = r#"[:find ?x :where [?x _ 9.95]]"#;
+    let SQLQuery { sql, args } = translate(&schema, input, None);
+
+    // In general, doubles _could_ be 1.0, which might match a boolean or a ref. Set tag = 5 to
+    // make sure we only match numbers.
+    assert_eq!(sql, "SELECT `datoms00`.e AS `?x` FROM `datoms` AS `datoms00` WHERE `datoms00`.v = 9.95 AND `datoms00`.value_type_tag = 5");
+    assert_eq!(args, vec![]);
+}
+
+#[test]
+fn test_unknown_attribute_integer_value() {
+    let schema = Schema::default();
+
+    let negative = r#"[:find ?x :where [?x _ -1]]"#;
+    let zero = r#"[:find ?x :where [?x _ 0]]"#;
+    let one = r#"[:find ?x :where [?x _ 1]]"#;
+    let two = r#"[:find ?x :where [?x _ 2]]"#;
+
+    // Can't match boolean; no need to filter it out.
+    let SQLQuery { sql, args } = translate(&schema, negative, None);
+    assert_eq!(sql, "SELECT `datoms00`.e AS `?x` FROM `datoms` AS `datoms00` WHERE `datoms00`.v = -1");
+    assert_eq!(args, vec![]);
+
+    // Excludes booleans.
+    let SQLQuery { sql, args } = translate(&schema, zero, None);
+    assert_eq!(sql, "SELECT `datoms00`.e AS `?x` FROM `datoms` AS `datoms00` WHERE (`datoms00`.v = 0 AND `datoms00`.value_type_tag <> 1)");
+    assert_eq!(args, vec![]);
+
+    // Excludes booleans.
+    let SQLQuery { sql, args } = translate(&schema, one, None);
+    assert_eq!(sql, "SELECT `datoms00`.e AS `?x` FROM `datoms` AS `datoms00` WHERE (`datoms00`.v = 1 AND `datoms00`.value_type_tag <> 1)");
+    assert_eq!(args, vec![]);
+
+    // Can't match boolean; no need to filter it out.
+    let SQLQuery { sql, args } = translate(&schema, two, None);
+    assert_eq!(sql, "SELECT `datoms00`.e AS `?x` FROM `datoms` AS `datoms00` WHERE `datoms00`.v = 2");
+    assert_eq!(args, vec![]);
+}
+
+#[test]
+fn test_unknown_ident() {
+    let schema = Schema::default();
+
+    let impossible = r#"[:find ?x :where [?x :db/ident :no/exist]]"#;
+    let parsed = parse_find_string(impossible).expect("parse failed");
+    let algebrized = algebrize(&schema, parsed);
+
+    // This query cannot return results: the ident doesn't resolve for a ref-typed attribute.
+    assert!(algebrized.is_known_empty());
+
+    // If you insist…
+    let select = query_to_select(algebrized);
+    let sql = select.query.to_sql_query().unwrap().sql;
+    assert_eq!("SELECT 1 LIMIT 0", sql);
+}

src/query.rs

@@ -66,6 +66,12 @@ pub fn q_once<'sqlite, 'schema, 'query, T, U>
 
     let parsed = parse_find_string(query)?;
     let mut algebrized = algebrize(schema, parsed);
+
+    if algebrized.is_known_empty() {
+        // We don't need to do any SQL work at all.
+        return Ok(QueryResults::empty(&algebrized.find_spec));
+    }
+
     algebrized.apply_limit(limit.into());
 
     let select = query_to_select(algebrized);