Fix loopbackio#1795 - Count issue with related models using though model

lib/scope.js

@@ -431,11 +431,51 @@ function defineScope(cls, targetClass, name, params, methods, options) {
       options = {};
     }
     options = options || {};
-
+    // If there is a through model
+    // run another query to apply filter on relatedModel(targetModel)
+    // see github.com/strongloop/loopback-datasource-juggler/issues/1795
+    let scopeOnRelatedModel = false;
+    let queryRelated;
+    if (this._scope && this._scope.collect &&
+      where !== null && typeof where === 'object') {
+      queryRelated = {
+        relation: this._scope.collect,
+        scope: {
+          where: where,
+        },
+      };
+      where = {};
+      scopeOnRelatedModel = true;
+    }
     const targetModel = definition.targetModel(this._receiver);
     const scoped = (this._scope && this._scope.where) || {};
     const filter = mergeQuery({where: scoped}, {where: where || {}});
-    return targetModel.destroyAll(filter.where, options, cb);
+    if (!scopeOnRelatedModel) {
+      return targetModel.destroyAll(filter.where, options, cb);
+    }
+    return targetModel.find(filter, options, function(err, findData) {
+      const relatedModel = targetModel.relations[queryRelated.relation].modelTo;
+      const keyFrom = targetModel.relations[queryRelated.relation].keyFrom;
+      const IdKey = idName(relatedModel);
+
+      // Merge queryRelated filter and targetId filter
+      const buildWhere = function() {
+        return {
+          and: [
+            {
+              [IdKey]: collectTargetIds(findData, keyFrom || IdKey),
+            },
+            queryRelated.scope.where],
+        };
+      };
+      if (queryRelated.scope.where !== undefined) {
+        queryRelated.scope.where = buildWhere();
+      } else {
+        queryRelated.scope.where = {};
+        queryRelated.scope.where[IdKey] = collectTargetIds(findData, keyFrom || IdKey);
+      }
+      return relatedModel.destroyAll(queryRelated.scope.where, options, cb);
+    });
   }
 
   function updateAll(where, data, options, cb) {

test/relations.test.js

@@ -702,6 +702,35 @@ describe('relations', function() {
       }
     });
 
+    it('should destroyAll all scoped record with promises based on related model properties', function(done) {
+      let id;
+      Physician.create()
+        .then(function(physician) {
+          return physician.patients.create({name: 'a'})
+            .then(function(ch) {
+              id = ch.id;
+              return physician.patients.create({name: 'z'});
+            })
+            .then(function() {
+              return physician.patients.create({name: 'c'});
+            })
+            .then(function() {
+              return verify(physician);
+            });
+        }).catch(done);
+
+      function verify(physician) {
+        return physician.patients.destroyAll({
+          name: 'a',
+        }, function(err, result) {
+          if (err) return done(err);
+          should.exist(result);
+          result.count.should.equal(1);
+          done();
+        });
+      }
+    });
+
     it('should build record on scope', function(done) {
       Physician.create(function(err, physician) {
         const patient = physician.patients.build();