grekker/cmdt-limit-bug

cMDT Relationship Query Bug

This repository is a bug repro for Salesforce Custom Metadata Types when using relationship queries and the LIMIT clause.

Undesirable Behavior

This query should limit the children per parent.

SELECT MasterLabel, (SELECT MasterLabel FROM Bars__r LIMIT 1) FROM Foo__mdt

However, it actually limits the entire set of children, so that one parent has a single child and all other parents have no children.

Reproducing

Defined in this repo are two custom metadata types Foo and Bar, with a relationship from Bar to Foo. There are a number of existing cMDT records in both types to facilitate showing the bug.

A single Apex class exists called Demo that can be called from anonymous Apex to demonstrate the bug. Here is the class:

public with sharing class Demo {

	public static void noLimit() {
		dump([SELECT MasterLabel, (SELECT MasterLabel FROM Bars__r) FROM Foo__mdt ORDER BY MasterLabel]);
	}

	public static void withLimit(Integer theLimit) {
		dump([SELECT MasterLabel, (SELECT MasterLabel FROM Bars__r LIMIT :theLimit) FROM Foo__mdt ORDER BY MasterLabel]);
	}

	private static void dump(List<Foo__mdt> foos) {
		for(Foo__mdt foo : foos) {
			String message = 'Foo: ' + foo.MasterLabel + '\n';
			for(Bar__mdt bar : foo.Bars__r) {
				message += '\tChild Bar: ' + bar.MasterLabel + '\n';
			}
			System.debug(LoggingLevel.WARN, message);
		}
	}
}

Here are some sample outputs:

Demo.noLimit();

15:00:07.29 (47299861)|USER_DEBUG|[17]|WARN|Foo: Foo1
	Child Bar: Foo1Bar4
	Child Bar: Foo1Bar2
	Child Bar: Foo1Bar3
	Child Bar: Foo1Bar1

15:00:07.29 (48652105)|USER_DEBUG|[17]|WARN|Foo: Foo2
	Child Bar: Foo2Bar2
	Child Bar: Foo2Bar1

15:00:07.29 (50219163)|USER_DEBUG|[17]|WARN|Foo: Foo3
	Child Bar: Foo2Bar3
	Child Bar: Foo3Bar1
	Child Bar: Foo3Bar2

Demo.withLimit(20);

15:00:40.53 (86781549)|USER_DEBUG|[17]|WARN|Foo: Foo1
	Child Bar: Foo1Bar4
	Child Bar: Foo1Bar2
	Child Bar: Foo1Bar3
	Child Bar: Foo1Bar1

15:00:40.53 (88958956)|USER_DEBUG|[17]|WARN|Foo: Foo2
	Child Bar: Foo2Bar2
	Child Bar: Foo2Bar1

15:00:40.53 (91248572)|USER_DEBUG|[17]|WARN|Foo: Foo3
	Child Bar: Foo2Bar3
	Child Bar: Foo3Bar1
	Child Bar: Foo3Bar2

Demo.withLimit(5);

15:01:06.30 (49240116)|USER_DEBUG|[17]|WARN|Foo: Foo1
	Child Bar: Foo1Bar4
	Child Bar: Foo1Bar2
	Child Bar: Foo1Bar3
	Child Bar: Foo1Bar1

15:01:06.30 (50139460)|USER_DEBUG|[17]|WARN|Foo: Foo2
	Child Bar: Foo2Bar2

15:01:06.30 (50662405)|USER_DEBUG|[17]|WARN|Foo: Foo3

Demo.withLimit(2);

15:01:31.28 (44578740)|USER_DEBUG|[17]|WARN|Foo: Foo1
	Child Bar: Foo1Bar4
	Child Bar: Foo1Bar2

15:01:31.28 (45043084)|USER_DEBUG|[17]|WARN|Foo: Foo2

15:01:31.28 (45425628)|USER_DEBUG|[17]|WARN|Foo: Foo3

Demo.withLimit(1);

15:01:54.35 (49885876)|USER_DEBUG|[17]|WARN|Foo: Foo1
	Child Bar: Foo1Bar4

15:01:54.35 (50350946)|USER_DEBUG|[17]|WARN|Foo: Foo2

15:01:54.35 (50759944)|USER_DEBUG|[17]|WARN|Foo: Foo3