mentat/src/query.rs

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// Copyright 2016 Mozilla
//
// Licensed under the Apache License, Version 2.0 (the "License"); you may not use
// this file except in compliance with the License. You may obtain a copy of the
// License at http://www.apache.org/licenses/LICENSE-2.0
// Unless required by applicable law or agreed to in writing, software distributed
// under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
// CONDITIONS OF ANY KIND, either express or implied. See the License for the
// specific language governing permissions and limitations under the License.
use rusqlite;
use rusqlite::types::ToSql;
use std::rc::Rc;
use core_traits::{
Entid,
KnownEntid,
};
use mentat_core::{
Binding,
HasSchema,
Schema,
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TypedValue,
};
use mentat_query_algebrizer::{
AlgebraicQuery,
EmptyBecause,
FindQuery,
algebrize_with_inputs,
parse_find_string,
};
pub use mentat_query_algebrizer::{
QueryInputs,
};
pub use mentat_query::{
Keyword,
PlainSymbol,
Variable,
};
use mentat_query::{
Element,
FindSpec,
Pattern,
PatternNonValuePlace,
PatternValuePlace,
WhereClause,
};
use mentat_query_projector::{
ConstantProjector,
Projector,
};
use mentat_sql::{
SQLQuery,
};
use mentat_query_translator::{
ProjectedSelect,
query_to_select,
};
pub use mentat_query_algebrizer::{
Known,
};
pub use mentat_query_projector::{
QueryOutput, // Includes the columns/find spec.
QueryResults, // The results themselves.
RelResult,
};
use errors::{
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MentatError,
Result,
};
pub type QueryExecutionResult = Result<QueryOutput>;
pub type PreparedResult<'sqlite> = Result<PreparedQuery<'sqlite>>;
pub enum PreparedQuery<'sqlite> {
Empty {
find_spec: Rc<FindSpec>,
},
Constant {
select: ConstantProjector,
},
Bound {
statement: rusqlite::Statement<'sqlite>,
schema: Schema,
connection: &'sqlite rusqlite::Connection,
args: Vec<(String, Rc<rusqlite::types::Value>)>,
projector: Box<Projector>,
},
}
impl<'sqlite> PreparedQuery<'sqlite> {
pub fn run<T>(&mut self, _inputs: T) -> QueryExecutionResult where T: Into<Option<QueryInputs>> {
match self {
&mut PreparedQuery::Empty { ref find_spec } => {
Ok(QueryOutput::empty(find_spec))
},
&mut PreparedQuery::Constant { ref select } => {
select.project_without_rows().map_err(|e| e.into())
},
&mut PreparedQuery::Bound { ref mut statement, ref schema, ref connection, ref args, ref projector } => {
let rows = run_statement(statement, args)?;
projector.project(schema, connection, rows)
.map_err(|e| e.into())
}
}
}
}
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pub trait IntoResult {
fn into_scalar_result(self) -> Result<Option<Binding>>;
fn into_coll_result(self) -> Result<Vec<Binding>>;
fn into_tuple_result(self) -> Result<Option<Vec<Binding>>>;
fn into_rel_result(self) -> Result<RelResult<Binding>>;
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}
impl IntoResult for QueryExecutionResult {
fn into_scalar_result(self) -> Result<Option<Binding>> {
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self?.into_scalar().map_err(|e| e.into())
}
fn into_coll_result(self) -> Result<Vec<Binding>> {
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self?.into_coll().map_err(|e| e.into())
}
fn into_tuple_result(self) -> Result<Option<Vec<Binding>>> {
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self?.into_tuple().map_err(|e| e.into())
}
fn into_rel_result(self) -> Result<RelResult<Binding>> {
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self?.into_rel().map_err(|e| e.into())
}
}
/// A struct describing information about how Mentat would execute a query.
pub enum QueryExplanation {
/// A query known in advance to be empty, and why we believe that.
KnownEmpty(EmptyBecause),
/// A query known in advance to return a constant value.
KnownConstant,
/// A query that takes actual work to execute.
ExecutionPlan {
/// The translated query and any bindings.
query: SQLQuery,
/// The output of SQLite's `EXPLAIN QUERY PLAN`.
steps: Vec<QueryPlanStep>,
},
}
/// A single row in the output of SQLite's `EXPLAIN QUERY PLAN`.
/// See https://www.sqlite.org/eqp.html for an explanation of each field.
pub struct QueryPlanStep {
pub select_id: i32,
pub order: i32,
pub from: i32,
pub detail: String,
}
fn algebrize_query<T>
(known: Known,
query: FindQuery,
inputs: T) -> Result<AlgebraicQuery>
where T: Into<Option<QueryInputs>>
{
let algebrized = algebrize_with_inputs(known, query, 0, inputs.into().unwrap_or(QueryInputs::default()))?;
let unbound = algebrized.unbound_variables();
// Because we are running once, we can check that all of our `:in` variables are bound at this point.
// If they aren't, the user has made an error -- perhaps writing the wrong variable in `:in`, or
// not binding in the `QueryInput`.
if !unbound.is_empty() {
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bail!(MentatError::UnboundVariables(unbound.into_iter().map(|v| v.to_string()).collect()));
}
Ok(algebrized)
}
fn fetch_values<'sqlite>
(sqlite: &'sqlite rusqlite::Connection,
known: Known,
entity: Entid,
attribute: Entid,
only_one: bool) -> QueryExecutionResult {
let v = Variable::from_valid_name("?v");
// This should never fail.
// TODO: it should be possible to algebrize with variable entity and attribute,
// particularly with known type, allowing the use of prepared statements.
let pattern = Pattern::simple(PatternNonValuePlace::Entid(entity),
PatternNonValuePlace::Entid(attribute),
PatternValuePlace::Variable(v.clone()))
.unwrap();
let element = Element::Variable(v);
let spec = if only_one { FindSpec::FindScalar(element) } else { FindSpec::FindColl(element) };
let query = FindQuery::simple(spec,
vec![WhereClause::Pattern(pattern)]);
let algebrized = algebrize_query(known, query, None)?;
run_algebrized_query(known, sqlite, algebrized)
}
fn lookup_attribute(schema: &Schema, attribute: &Keyword) -> Result<KnownEntid> {
schema.get_entid(attribute)
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.ok_or_else(|| MentatError::UnknownAttribute(attribute.name().into()).into())
}
/// Return a single value for the provided entity and attribute.
/// If the attribute is multi-valued, an arbitrary value is returned.
/// If no value is present for that entity, `None` is returned.
/// If `attribute` isn't an attribute, `None` is returned.
pub fn lookup_value<'sqlite, 'schema, 'cache, E, A>
(sqlite: &'sqlite rusqlite::Connection,
known: Known,
entity: E,
attribute: A) -> Result<Option<TypedValue>>
where E: Into<Entid>,
A: Into<Entid> {
let entid = entity.into();
let attrid = attribute.into();
if known.is_attribute_cached_forward(attrid) {
Ok(known.get_value_for_entid(known.schema, attrid, entid).cloned())
} else {
fetch_values(sqlite, known, entid, attrid, true)
.into_scalar_result()
// Safe to unwrap: we never retrieve structure.
.map(|r| r.map(|v| v.into_scalar().unwrap()))
}
}
pub fn lookup_values<'sqlite, E, A>
(sqlite: &'sqlite rusqlite::Connection,
known: Known,
entity: E,
attribute: A) -> Result<Vec<TypedValue>>
where E: Into<Entid>,
A: Into<Entid> {
let entid = entity.into();
let attrid = attribute.into();
if known.is_attribute_cached_forward(attrid) {
Ok(known.get_values_for_entid(known.schema, attrid, entid)
.cloned()
.unwrap_or_else(|| vec![]))
} else {
fetch_values(sqlite, known, entid, attrid, false)
.into_coll_result()
// Safe to unwrap: we never retrieve structure.
.map(|v| v.into_iter().map(|x| x.into_scalar().unwrap()).collect())
}
}
/// Return a single value for the provided entity and attribute.
/// If the attribute is multi-valued, an arbitrary value is returned.
/// If no value is present for that entity, `None` is returned.
/// If `attribute` doesn't name an attribute, an error is returned.
pub fn lookup_value_for_attribute<'sqlite, 'attribute, E>
(sqlite: &'sqlite rusqlite::Connection,
known: Known,
entity: E,
attribute: &'attribute Keyword) -> Result<Option<TypedValue>>
where E: Into<Entid> {
let attribute = lookup_attribute(known.schema, attribute)?;
lookup_value(sqlite, known, entity.into(), attribute)
}
pub fn lookup_values_for_attribute<'sqlite, 'attribute, E>
(sqlite: &'sqlite rusqlite::Connection,
known: Known,
entity: E,
attribute: &'attribute Keyword) -> Result<Vec<TypedValue>>
where E: Into<Entid> {
let attribute = lookup_attribute(known.schema, attribute)?;
lookup_values(sqlite, known, entity.into(), attribute)
}
fn run_statement<'sqlite, 'stmt, 'bound>
(statement: &'stmt mut rusqlite::Statement<'sqlite>,
bindings: &'bound [(String, Rc<rusqlite::types::Value>)]) -> Result<rusqlite::Rows<'stmt>> {
let rows = if bindings.is_empty() {
statement.query(&[])?
} else {
let refs: Vec<(&str, &ToSql)> =
bindings.iter()
.map(|&(ref k, ref v)| (k.as_str(), v.as_ref() as &ToSql))
.collect();
statement.query_named(&refs)?
};
Ok(rows)
}
fn run_sql_query<'sqlite, 'sql, 'bound, T, F>
(sqlite: &'sqlite rusqlite::Connection,
sql: &'sql str,
bindings: &'bound [(String, Rc<rusqlite::types::Value>)],
mut mapper: F) -> Result<Vec<T>>
where F: FnMut(&rusqlite::Row) -> T
{
let mut statement = sqlite.prepare(sql)?;
let mut rows = run_statement(&mut statement, &bindings)?;
let mut result = vec![];
while let Some(row_or_error) = rows.next() {
result.push(mapper(&row_or_error?));
}
Ok(result)
}
fn algebrize_query_str<'query, T>
(known: Known,
query: &'query str,
inputs: T) -> Result<AlgebraicQuery>
where T: Into<Option<QueryInputs>> {
let parsed = parse_find_string(query)?;
algebrize_query(known, parsed, inputs)
}
fn run_algebrized_query<'sqlite>
(known: Known,
sqlite: &'sqlite rusqlite::Connection,
algebrized: AlgebraicQuery) -> QueryExecutionResult {
assert!(algebrized.unbound_variables().is_empty(),
"Unbound variables should be checked by now");
if algebrized.is_known_empty() {
// We don't need to do any SQL work at all.
return Ok(QueryOutput::empty(&algebrized.find_spec));
}
let select = query_to_select(known.schema, algebrized)?;
match select {
ProjectedSelect::Constant(constant) => {
constant.project_without_rows()
.map_err(|e| e.into())
},
ProjectedSelect::Query { query, projector } => {
let SQLQuery { sql, args } = query.to_sql_query()?;
let mut statement = sqlite.prepare(sql.as_str())?;
let rows = run_statement(&mut statement, &args)?;
projector.project(known.schema, sqlite, rows).map_err(|e| e.into())
},
}
}
/// Take an EDN query string, a reference to an open SQLite connection, a Mentat schema, and an
/// optional collection of input bindings (which should be keyed by `"?varname"`), and execute the
/// query immediately, blocking the current thread.
/// Returns a structure that corresponds to the kind of input query, populated with `TypedValue`
/// instances.
/// The caller is responsible for ensuring that the SQLite connection has an open transaction if
/// isolation is required.
pub fn q_once<'sqlite, 'query, T>
(sqlite: &'sqlite rusqlite::Connection,
known: Known,
query: &'query str,
inputs: T) -> QueryExecutionResult
where T: Into<Option<QueryInputs>>
{
let algebrized = algebrize_query_str(known, query, inputs)?;
run_algebrized_query(known, sqlite, algebrized)
}
/// Just like `q_once`, but doesn't use any cached values.
pub fn q_uncached<'sqlite, 'schema, 'query, T>
(sqlite: &'sqlite rusqlite::Connection,
schema: &'schema Schema,
query: &'query str,
inputs: T) -> QueryExecutionResult
where T: Into<Option<QueryInputs>>
{
let known = Known::for_schema(schema);
let algebrized = algebrize_query_str(known, query, inputs)?;
run_algebrized_query(known, sqlite, algebrized)
}
pub fn q_prepare<'sqlite, 'schema, 'cache, 'query, T>
(sqlite: &'sqlite rusqlite::Connection,
known: Known<'schema, 'cache>,
query: &'query str,
inputs: T) -> PreparedResult<'sqlite>
where T: Into<Option<QueryInputs>>
{
let algebrized = algebrize_query_str(known, query, inputs)?;
let unbound = algebrized.unbound_variables();
if !unbound.is_empty() {
// TODO: Allow binding variables at execution time, not just
// preparation time.
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bail!(MentatError::UnboundVariables(unbound.into_iter().map(|v| v.to_string()).collect()));
}
if algebrized.is_known_empty() {
// We don't need to do any SQL work at all.
return Ok(PreparedQuery::Empty {
find_spec: algebrized.find_spec,
});
}
let select = query_to_select(known.schema, algebrized)?;
match select {
ProjectedSelect::Constant(constant) => {
Ok(PreparedQuery::Constant {
select: constant,
})
},
ProjectedSelect::Query { query, projector } => {
let SQLQuery { sql, args } = query.to_sql_query()?;
let statement = sqlite.prepare(sql.as_str())?;
Ok(PreparedQuery::Bound {
statement,
schema: known.schema.clone(),
connection: sqlite,
args,
projector: projector
})
},
}
}
pub fn q_explain<'sqlite, 'query, T>
(sqlite: &'sqlite rusqlite::Connection,
known: Known,
query: &'query str,
inputs: T) -> Result<QueryExplanation>
where T: Into<Option<QueryInputs>>
{
let algebrized = algebrize_query_str(known, query, inputs)?;
if algebrized.is_known_empty() {
return Ok(QueryExplanation::KnownEmpty(algebrized.cc.empty_because.unwrap()));
}
match query_to_select(known.schema, algebrized)? {
ProjectedSelect::Constant(_constant) => Ok(QueryExplanation::KnownConstant),
ProjectedSelect::Query { query, projector: _projector } => {
let query = query.to_sql_query()?;
let plan_sql = format!("EXPLAIN QUERY PLAN {}", query.sql);
let steps = run_sql_query(sqlite, &plan_sql, &query.args, |row| {
QueryPlanStep {
select_id: row.get(0),
order: row.get(1),
from: row.get(2),
detail: row.get(3)
}
})?;
Ok(QueryExplanation::ExecutionPlan { query, steps })
},
}
}