feat: access the node instance in custom validation

README.md

@@ -603,6 +603,8 @@ If you have custom validation logic you can create a _Constraint class_:
    which defines validation logic. If validation succeeds, method returns true, otherwise false.
    Custom validator can be asynchronous, if you want to perform validation after some asynchronous
    operations, simply return a promise with boolean inside in `validate` method.
+   `ValidationArguments` contains useful information about validation process, like object that is being validated,
+   or the current object instance to validate value based on parent nodes.
 
    Also we defined optional method `defaultMessage` which defines a default error message,
    in the case that the decorator's implementation doesn't set an error message.

src/validation/ValidationArguments.ts

@@ -23,6 +23,11 @@ export interface ValidationArguments {
    */
   object: object;
 
+  /**
+   * Instance of the object being validated.
+   */
+  instance: object;
+
   /**
    * Name of the object's property being validated.
    */

src/validation/ValidationExecutor.ts

@@ -24,6 +24,7 @@ export class ValidationExecutor {
   // Private Properties
   // -------------------------------------------------------------------------
 
+  private instance: any = undefined;
   private metadataStorage = getMetadataStorage();
 
   // -------------------------------------------------------------------------
@@ -51,6 +52,11 @@ export class ValidationExecutor {
       );
     }
 
+    // Keep the instance to the original object
+    if (this.instance === undefined){
+      this.instance = object;
+    }
+
     const groups = this.validatorOptions ? this.validatorOptions.groups : undefined;
     const strictGroups = (this.validatorOptions && this.validatorOptions.strictGroups) || false;
     const always = (this.validatorOptions && this.validatorOptions.always) || false;
@@ -263,6 +269,7 @@ export class ValidationExecutor {
           targetName: object.constructor ? (object.constructor as any).name : undefined,
           property: metadata.propertyName,
           object: object,
+          instance: this.instance,
           value: value,
           constraints: metadata.constraints,
         };
@@ -405,6 +412,7 @@ export class ValidationExecutor {
       property: metadata.propertyName,
       object: object,
       value: value,
+      instance: this.instance,
       constraints: metadata.constraints,
     };