Winter 19 release provides ability to instantiate the custom metadata in apex .This seems to be useful to generate data for test classes .

However when we have metadata relationship entity or field entity relationship the QualifiedName comes as null in Test class .

Lets take an example with the below code in a Test class .For now use execute Anonymous via Dev console

Relationship__mdt relationship = new Relationship__mdt(
        DeveloperName = 'Test',
        Active__c = true,
        Object__c = 'Account',
        AccountRelationship__c = 'ParentId'

In the above code Object__c is of type metadataRelationship (Object definition ) and AccountRelationship__c is also of metadataRelationship type (Field Entity Definition) .

When i do relationship.Object__r.QualifiedAPIName in test context I receive null and not 'Account'.

Similarly when i do relationship.AccountRelationship__r.QualifiedAPIName in test context I receive null and not ParentId .

This makes it not helpful again for use cases where metadata data has entity relationship and the code uses QualifiedName .

Is it a bug or I am overlooking something ?

  • I've never observed this problem. What instance are you on?
    – Adrian Larson
    Nov 20, 2018 at 16:03
  • Sandbox instance and note this issue is in test class Nov 20, 2018 at 16:04
  • No I mean cs10, cs20, etc. Also are you actually able to construct a record or is that just pseudo-code to illustrate?
    – Adrian Larson
    Nov 20, 2018 at 16:06
  • 6
    relationships are not automatically populated, you have to query for them. Also, all the fields you need to use are read-only, so you would have to either create a big JSON string to fake the relationship, or you'll have to use the stub API/dependency injection.
    – sfdcfox
    Nov 20, 2018 at 16:17
  • 3
    Last I checked you could not even construct Custom Metadata records. This is the first I've seen of that change.
    – Adrian Larson
    Nov 20, 2018 at 16:20

1 Answer 1


You still need to use JSON construction if you want to set parent attributes without a true query for the records.

Non Functional Code

EntityDefinition sourceObject = [SELECT QualifiedApiName FROM EntityDefinition LIMIT 1];
MyMapping__mdt mapping = new MyMapping__mdt(
    Source_Object__r = sourceObject


Field is not writeable: MyMapping__mdt.Source_Object__r

Functional Code

Map<String, Object> mockMapping = new Map<String, Object>
    'attributes' => new Map<String, Object>
        'type' => 'MyMapping__mdt '
    'Source_Object__r' => new Map<String, Object>
        'attributes' => new Map<String, Object>
            'type' => 'EntityDefinition'
        'QualifiedApiName' => 'Account'
MyMapping__mdt mapping = (MyMapping__mdt)JSON.deserialize(
    JSON.serialize(mockMapping), MyMapping__mdt.class



  • 1
    Thanks for the response .I just feel this should be natively supported Nov 20, 2018 at 21:19
  • 3
    Perhaps it will come in future releases. It was a pretty big change just to allow construction of Custom Metadata at all.
    – Adrian Larson
    Nov 20, 2018 at 21:45

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