[SalesForce] Getting “__r” relationship name from Schema.SObjectType.Fields

Say I have a master-detail relationship between two objects, Schematic__c and Part__c.

I can SOQL query the master from the detail: [SELECT Schematic__r.Name FROM Part__c]

If I'm building a query from strings, I resolve the schema name, for example in a managed package:

SObjectType.Part__c.Fields.Schematic__c.Name //gives me 'ns__Schematic__c'

But when traversing into the master object, the __r relationship suffix is what I need to surface. I've toyed around with the obvious Schema.SObjectType variations but I'm not having much luck:

SObjectType.Part__c.Fields.Schematic__r.Name //Schematic__r is not a field of ns__Symbol__c

What's the correct way to resolve the ns__Schematic__r.Name token without replacing the suffix?

Best Answer

No no, the field (API) name is Schematic__c, you need to start from it. Think about Schematic__r (the rel. name) like a consistent table alias when you'd make JOINs in regular database, nothing more.

To go "up":

Schema.DescribeFieldResult f = Schema.sObjectType.Order_Line_Item__c.fields.Order__c;
System.debug(f.getRelationshipName()); 
// Outputs "Order__r", also with namespace if you have one

(You could also play with checking f.getType() == Schema.DisplayType.REFERENCE if you need to describe all fields and wonder which ones are lookups)

to go "down":

for(Schema.ChildRelationship cr : Order__c.SObjectType.getDescribe().getChildRelationships()){
    System.debug(cr.getChildSObject() + '.' + cr.getField() + ' reversed is: ' + cr.getRelationshipName());
}

ActivityHistory.WhatId reversed is: ActivityHistories
Attachment.ParentId reversed is: Attachments
ContentDocumentLink.LinkedEntityId reversed is: null
ContentVersion.FirstPublishLocationId reversed is: null
(...)
Order_Line_item__c.Order__c reversed is: Order_Line_items__r    // bingo
Order__History.ParentId reversed is: Histories
(...)
Task.WhatId reversed is: Tasks

Related Solutions

[SalesForce] From Parent ID, dynamically derive child’s lookup field name/token

As I understand the question, for a given child sObject and a given parent (lookup) object's ID, how do you locate the child object's lookup field name or token?

In your example,

Employee__c has several lookup fields to several parents. If you have some parentId, you can easily get the SObjectType of the parent with parentId.getSobjectType() but what is the corresponding fieldname/token in Employee__c?

There's no way to derive this dynamically from the describe information reliably because a given child SObject can have multiple lookup fields to the same parent SObject.

A classic example of this in Opportunity wherein I often see folks adding lookup fields to key Contacts such as BillToContact__c and ShipToContact__c (rather than using OpportunityContactRole which has some challenges for other reasons)

If you had an Opportunity and an ID of some Contact, which of the two Opportunity lookup fields to Contact do you try and set with the someContactId?

You can't, because it is the relationship name that tells you which lookup field to use and the relationship name can't be derived from someContactId

As you stated in your comment, in a limited application wherein you guaranteed that there were never multiple lookup fields to the same parent, you could build a map of:

map<SobjectType,SobjectField> parentTypeToChildFldTokenMap

and then you could look up the field token of the child object with:

SobjectField fldToken = parentTypeToChildFldTokenMap.get(someParentId.getSObjectType());

Otherwise, the application needs to know which relationship the someParentId participates in to ascertain the child fieldToken. Then, you would go to the parent's Describe result and loop through the ChildRelationships looking for a match on relationshipname. The ChildRelationship object contains the fieldtoken of the child lookup field.

[SalesForce] Want to fetch the child relationship name from the Lookup field name

No, you need to loop through the parent describe.

for (ChildRelationship relation : SObjectType.Lead.getChildRelationships())
    if (relation.getField() == MyObject__c.MyLookup__c)
        String relationshipName = relation.getRelationshipName();

You should do this processing before you enter your loop, not each iteration.

Best Answer

Related Solutions

[SalesForce] From Parent ID, dynamically derive child’s lookup field name/token

[SalesForce] Want to fetch the child relationship name from the Lookup field name

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