QueryCompiler

A compiler phase which partitions a query for execution by multiple composed interpreters.

This phase transforms the input query by assigning subtrees to component interpreters as specified by the supplied mapping.

The mapping has Type and field name pairs as keys and component id and join function pairs as values. When the traversal of the input query visits a Select node with type Type.field name it will replace the Select with a Component node comprising,

1. the component id of the interpreter which will be responsible for evaluating the subquery.
2. A join function which will be called during interpretation with,

i) the cursor at that point in evaluation. ii) The deferred subquery.

This join function is responsible for computing the continuation query which will be evaluated by the responsible interpreter.

Because the join is provided with the cursor of the parent interpreter the subquery can be parameterised with values derived from the parent query.

A QueryCompiler phase.

A compiler phase which translates Select nodes to be directly interpretable.

This phase,

1. types bindings according to the schema: i) untyped enums are validated and typed according to their declared type. ii) String and Int bindings are translated to ID bindings where appropriate. iii) default values are supplied for missing arguments. iv) arguments are permuted into the order declared in the schema.

2. eliminates Select arguments by delegating to a model-specific PartialFunction which is responsible for translating Select nodes into a form which is directly interpretable, replacing them with a Filter or Unique node with a Predicate which is parameterized by the arguments, eg.

  Select("character", List(IDBinding("id", "1000")), child)

might be translated to,

  Filter(FieldEquals("id", "1000"), child)

3. types narrowing coercions by resolving the target type against the schema.

4. verifies that leaves have an empty subselection set and that structured types have a non-empty subselection set.

5. eliminates Skipped nodes.