fix: add validation support for Union schema types

lib/document.js

@@ -2808,13 +2808,14 @@ function _getPathsToValidate(doc, pathsToValidate, pathsToSkip, isNestedValidate
 
     // Optimization: if primitive path with no validators, or array of primitives
     // with no validators, skip validating this path entirely.
-    if (!_pathType.caster && _pathType.validators.length === 0 && !_pathType.$parentSchemaDocArray) {
+    if (!_pathType.caster && _pathType.validators.length === 0 && !_pathType.$parentSchemaDocArray && _pathType.instance !== 'Union') {
       paths.delete(path);
     } else if (_pathType.$isMongooseArray &&
       !_pathType.$isMongooseDocumentArray && // Skip document arrays...
       !_pathType.$embeddedSchemaType.$isMongooseArray && // and arrays of arrays
       _pathType.validators.length === 0 && // and arrays with top-level validators
-      _pathType.$embeddedSchemaType.validators.length === 0) {
+      _pathType.$embeddedSchemaType.validators.length === 0 &&
+      _pathType.$embeddedSchemaType.instance !== 'Union') {
       paths.delete(path);
     }
   }

lib/schema/union.js

@@ -20,11 +20,21 @@ class Union extends SchemaType {
       throw new Error('Union schema type requires an array of types');
     }
     this.schemaTypes = options.of.map(obj => options.parentSchema.interpretAsType(key, obj, schemaOptions));
+
+    this.validators.push({
+      validator: () => true,
+      type: 'union'
+    });
   }
 
   cast(val, doc, init, prev, options) {
     let firstValue = firstValueSymbol;
     let lastError;
+    let bestMatch = null;
+    let bestMatchScore = -1;
+
+    const isObject = val != null && typeof val === 'object' && !Array.isArray(val);
+
     // Loop through each schema type in the union. If one of the schematypes returns a value that is `=== val`, then
     // use `val`. Otherwise, if one of the schematypes casted successfully, use the first successfully casted value.
     // Finally, if none of the schematypes casted successfully, throw the error from the last schema type in the union.
@@ -36,13 +46,30 @@ class Union extends SchemaType {
         if (casted === val) {
           return casted;
         }
+
+        if (isObject && casted != null && typeof casted === 'object') {
+          const inputKeys = Object.keys(val);
+          const preservedFields = inputKeys.filter(key => key in casted && key !== '_id').length;
+          const score = preservedFields;
+
+          if (score > bestMatchScore) {
+            bestMatchScore = score;
+            bestMatch = casted;
+          }
+        }
+
         if (firstValue === firstValueSymbol) {
           firstValue = casted;
         }
       } catch (error) {
         lastError = error;
       }
     }
+
+    if (bestMatch !== null) {
+      return bestMatch;
+    }
+
     if (firstValue !== firstValueSymbol) {
       return firstValue;
     }
@@ -53,6 +80,11 @@ class Union extends SchemaType {
   applySetters(val, doc, init, prev, options) {
     let firstValue = firstValueSymbol;
     let lastError;
+    let bestMatch = null;
+    let bestMatchScore = -1;
+
+    const isObject = val != null && typeof val === 'object' && !Array.isArray(val);
+
     // Loop through each schema type in the union. If one of the schematypes returns a value that is `=== val`, then
     // use `val`. Otherwise, if one of the schematypes casted successfully, use the first successfully casted value.
     // Finally, if none of the schematypes casted successfully, throw the error from the last schema type in the union.
@@ -69,13 +101,31 @@ class Union extends SchemaType {
         if (castedVal === val) {
           return castedVal;
         }
+
+
+        if (isObject && castedVal != null && typeof castedVal === 'object') {
+          const inputKeys = Object.keys(val);
+          const preservedFields = inputKeys.filter(key => key in castedVal && key !== '_id').length;
+          const score = preservedFields;
+
+          if (score > bestMatchScore) {
+            bestMatchScore = score;
+            bestMatch = castedVal;
+          }
+        }
+
         if (firstValue === firstValueSymbol) {
           firstValue = castedVal;
         }
       } catch (error) {
         lastError = error;
       }
     }
+
+    if (bestMatch !== null) {
+      return bestMatch;
+    }
+
     if (firstValue !== firstValueSymbol) {
       return firstValue;
     }
@@ -88,6 +138,108 @@ class Union extends SchemaType {
     schematype.schemaTypes = this.schemaTypes.map(schemaType => schemaType.clone());
     return schematype;
   }
+
+  /**
+   * Validates the value against all schema types in the union.
+   * The value must successfully validate against at least one schema type.
+   *
+   * @api private
+   */
+  doValidate(value, fn, scope, options) {
+    if (options && options.skipSchemaValidators) {
+      return fn(null);
+    }
+
+    SchemaType.prototype.doValidate.call(this, value, function(error) {
+      if (error) {
+        return fn(error);
+      }
+      if (value == null) {
+        return fn(null);
+      }
+
+      if (value && value.schema && value.$__) {
+        const subdocSchema = value.schema;
+        for (let i = 0; i < this.schemaTypes.length; ++i) {
+          const schemaType = this.schemaTypes[i];
+          if (schemaType.schema && schemaType.schema === subdocSchema) {
+            return schemaType.doValidate(value, fn, scope, options);
+          }
+        }
+      }
+      const validationErrors = [];
+      let callbackCalled = false;
+      let completed = 0;
+
+      for (let i = 0; i < this.schemaTypes.length; ++i) {
+        const schemaType = this.schemaTypes[i];
+
+        schemaType.doValidate(value, (err) => {
+          if (callbackCalled) {
+            return;
+          }
+
+          completed++;
+
+          if (!err) {
+            callbackCalled = true;
+            return fn(null);
+          }
+
+          validationErrors.push(err);
+
+          if (completed === this.schemaTypes.length) {
+            callbackCalled = true;
+            return fn(validationErrors[0]);
+          }
+        }, scope, options);
+      }
+    }.bind(this), scope, options);
+  }
+
+  /**
+   * Synchronously validates the value against all schema types in the union.
+   * The value must successfully validate against at least one schema type.
+   *
+   * @api private
+   */
+  doValidateSync(value, scope, options) {
+    if (!options || !options.skipSchemaValidators) {
+      const schemaTypeError = SchemaType.prototype.doValidateSync.call(this, value, scope);
+      if (schemaTypeError) {
+        return schemaTypeError;
+      }
+    }
+
+    if (value == null) {
+      return;
+    }
+
+    if (value && value.schema && value.$__) {
+      const subdocSchema = value.schema;
+      for (let i = 0; i < this.schemaTypes.length; ++i) {
+        const schemaType = this.schemaTypes[i];
+        if (schemaType.schema && schemaType.schema === subdocSchema) {
+          return schemaType.doValidateSync(value, scope, options);
+        }
+      }
+    }
+
+    const validationErrors = [];
+
+    for (let i = 0; i < this.schemaTypes.length; ++i) {
+      const schemaType = this.schemaTypes[i];
+
+      const err = schemaType.doValidateSync(value, scope, options);
+      if (!err) {
+        return null;
+      }
+
+      validationErrors.push(err);
+    }
+
+    return validationErrors[0];
+  }
 }
 
 /**