WIP: pull

query-projector/src/lib.rs

@@ -66,6 +66,7 @@ use mentat_query_sql::{
 
 mod aggregates;
 mod project;
+mod pull;
 pub mod errors;
 
 pub use aggregates::{

query-projector/src/pull.rs

@@ -0,0 +1,87 @@
+// Copyright 2018 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 std::collections::{
+    BTreeSet,
+};
+
+use indexmap::{
+    IndexMap,
+    IndexSet,
+};
+
+use mentat_core::{
+    Entid,
+    SQLValueType,
+    SQLValueTypeSet,
+    TypedValue,
+    ValueType,
+    ValueTypeSet,
+};
+
+use mentat_core::util::{
+    Either,
+};
+
+use mentat_query::{
+    Element,
+    Variable,
+};
+
+use mentat_query_algebrizer::{
+    AlgebraicQuery,
+    ColumnName,
+    ConjoiningClauses,
+    QualifiedAlias,
+    VariableColumn,
+};
+
+
+use mentat_query_sql::{
+    ColumnOrExpression,
+    GroupBy,
+    Name,
+    Projection,
+    ProjectedColumn,
+};
+
+use aggregates::{
+    SimpleAggregation,
+    projected_column_for_simple_aggregate,
+};
+
+use errors::{
+    ErrorKind,
+    Result,
+};
+
+use super::{
+    TypedIndex,
+};
+
+/// A pull expression expands a binding into a structure. The returned structure
+/// associates attributes named in the input or retrieved from the store with values.
+/// This association is a `StructuredMap`.
+struct StructuredMap {
+    attrs: IndexMap<Entid, StructuredValue>,
+}
+
+/// The values stored in a `StructuredMap` can be:
+/// * Vecs of structured values, for multi-valued component attributes or nested expressions.
+/// * Vecs of typed values, for multi-valued simple attributes. Unlike Datomic, Mentat can express
+///   an entity without a `{:db/id 12345678}` map.
+/// * Single structured values, for single-valued component attributes or nested expressions.
+/// * Single typed values, for simple attributes.
+enum StructuredValue {
+    Value(TypedValue),
+    Values(Vec<TypedValue>),
+    Structure(StructuredMap),
+    Structures(Vec<StructuredMap>),
+}