Add returnType util for satisfiability

src/query/index.js

@@ -7,6 +7,14 @@ import {
 } from '/src/sources/returns.js';
 import * as status from '/src/status';
 
+/**
+ * Query represents an API query to be resolved by the resolver. It is generated
+ * directly from a model and contains thing such as fields required, parameters,
+ * and whether we're loading a single item or a list.
+ *
+ * Queries are added to the resolver via the @load component and manager. It is
+ * the resolver's responsibility to identify which sources satisfy the query.
+ */
 export default class Query {
 
   status = status.PENDING

src/resolver/utils.js

@@ -1,6 +1,10 @@
 'use strict';
 
-import Returns, { RETURNS_ALL_FIELDS } from '/src/sources/returns';
+import Returns, {
+  RETURNS_ITEM,
+  RETURNS_LIST,
+  RETURNS_ALL_FIELDS
+} from '/src/sources/returns';
 
 /**
  * Predicate which checks that a given query contains all required params
@@ -66,6 +70,19 @@ export function doesSourceSatisfyAllQueryFields(source, query) {
   return query.fields.every(f => source.returns.fieldsAsObject[f] !== undefined);
 }
 
+/**
+ * If the query requires an item but the source only returns a list this returns
+ * false.
+ *
+ */
+export function doesSourceSatisfyQueryReturnType(source, query) {
+  if (source.returns.returnType === RETURNS_ITEM
+    && query.returnType === RETURNS_LIST) {
+    return false;
+  }
+  return true;
+}
+
 // TODO:
 // - `doesSourceSatisfySomeQueryFields` for partial matching
 // - How will we handle relationships within a query?

test/specs/resolver/utils.js

@@ -164,4 +164,19 @@ describe('resolver utils', () => {
     });
   });
 
+  describe('doesSourceSatisfyQueryReturnType', () => {
+    it('returns false if the query returns a list and the source returns an item', () => {
+      const s = new SourceDefinition({
+        id: 1,
+        returns: User.item(),
+        meta: {}
+      });
+      const q = new Query(
+        User,
+        ['id'],
+        RETURNS_LIST
+      );
+      assert.isFalse(utils.doesSourceSatisfyQueryReturnType(s, q));
+    });
+  });
 });