fix: relax constrain check to allow input containing constrained values

Consider a Product constraint like `{categoryId: 1}` and a request
to update (patch) Product with the following data:

    {
      name: 'updated',
      categoryId: 1
    }

Before this change, such request would be incorrectly rejected.

With this change in place, such requests are allowed.

packages/repository/src/__tests__/unit/repositories/constraint-utils.unit.ts

@@ -5,14 +5,14 @@
 
 import {expect} from '@loopback/testlab';
 import {
-  FilterBuilder,
-  Filter,
-  Where,
-  constrainFilter,
-  constrainWhere,
   constrainDataObject,
   constrainDataObjects,
+  constrainFilter,
+  constrainWhere,
   Entity,
+  Filter,
+  FilterBuilder,
+  Where,
 } from '../../..';
 
 describe('constraint utility functions', () => {
@@ -87,24 +87,58 @@ describe('constraint utility functions', () => {
       });
     });
 
-    it('throws error when the query changes field in constrain', () => {
+    it('throws error when the query changes field in constraint', () => {
       const input = new Order({id: 1, description: 'order 1'});
       const constraint: Partial<Order> = {id: 2};
       expect(() => {
         constrainDataObject(input, constraint);
       }).to.throwError(/Property "id" cannot be changed!/);
     });
 
+    it('allows constrained fields with the same values', () => {
+      const input = new Order({id: 2, description: 'order 1'});
+      const constraint: Partial<Order> = {id: 2};
+      const result = constrainDataObject(input, constraint);
+      expect(result).to.deepEqual(
+        new Order({
+          id: 2,
+          description: 'order 1',
+        }),
+      );
+    });
+  });
+
+  describe('constrainDataObjects', () => {
     it('constrains array of data objects', () => {
       const input = [
-        new Order({id: 1, description: 'order 1'}),
-        new Order({id: 2, description: 'order 2'}),
+        new Order({description: 'order 1'}),
+        new Order({description: 'order 2'}),
       ];
       const constraint: Partial<Order> = {id: 3};
       const result = constrainDataObjects(input, constraint);
       expect(result[0]).to.containDeep(Object.assign({}, input[0], constraint));
       expect(result[1]).to.containDeep(Object.assign({}, input[1], constraint));
     });
+
+    it('throws error when the query changes field in constraint', () => {
+      const input = [new Order({id: 1, description: 'order 1'})];
+      const constraint: Partial<Order> = {id: 2};
+      expect(() => {
+        constrainDataObjects(input, constraint);
+      }).to.throwError(/Property "id" cannot be changed!/);
+    });
+
+    it('allows constrained fields with the same values', () => {
+      const input = [new Order({id: 2, description: 'order 1'})];
+      const constraint: Partial<Order> = {id: 2};
+      const result = constrainDataObjects(input, constraint);
+      expect(result).to.deepEqual([
+        new Order({
+          id: 2,
+          description: 'order 1',
+        }),
+      ]);
+    });
   });
 
   /*---------------HELPERS----------------*/

packages/repository/src/repositories/constraint-utils.ts

@@ -3,10 +3,10 @@
 // This file is licensed under the MIT License.
 // License text available at https://opensource.org/licenses/MIT
 
-import {Filter, WhereBuilder, Where, FilterBuilder} from '../query';
-import {AnyObject, DataObject} from '../common-types';
 import {cloneDeep} from 'lodash';
+import {AnyObject, DataObject} from '../common-types';
 import {Entity} from '../model';
+import {Filter, FilterBuilder, Where, WhereBuilder} from '../query';
 
 /**
  * A utility function which takes a filter and enforces constraint(s)
@@ -55,12 +55,16 @@ export function constrainDataObject<T extends Entity>(
 ): DataObject<T> {
   const constrainedData = cloneDeep(originalData);
   for (const c in constraint) {
-    if (constrainedData.hasOwnProperty(c))
+    if (constrainedData.hasOwnProperty(c)) {
+      // Known limitation: === does not work for objects such as ObjectId
+      if (originalData[c] === constraint[c]) continue;
       throw new Error(`Property "${c}" cannot be changed!`);
+    }
     (constrainedData as AnyObject)[c] = constraint[c];
   }
   return constrainedData;
 }
+
 /**
  * A utility function which takes an array of model instance data and
  * enforces constraint(s) on it
@@ -71,13 +75,7 @@ export function constrainDataObject<T extends Entity>(
  */
 export function constrainDataObjects<T extends Entity>(
   originalData: DataObject<T>[],
-  constraint: Partial<T>,
+  constraint: DataObject<T>,
 ): DataObject<T>[] {
-  const constrainedData = cloneDeep(originalData);
-  for (let obj of constrainedData) {
-    for (let prop in constraint) {
-      (obj as AnyObject)[prop] = constraint[prop];
-    }
-  }
-  return constrainedData;
+  return originalData.map(obj => constrainDataObject(obj, constraint));
 }