SOQL statements cannot query more than 20 different child types error

Question

I have the following piece of code

 public static void fetchRelatedRecords(String primaryRecordString){
    SObject primaryRecord = (SObject)JSON.deserialize(primaryRecordString, SObject.class);
    String recordId = (String)primaryRecord.get('Id');
    Map<String, Schema.SobjectType> keys = new Map<String, Schema.SobjectType>();
    Map<String, Schema.SobjectType> describe = Schema.getGlobalDescribe();
    for(String s : describe.keyset()){
        keys.put(describe.get(s).getDescribe().getKeyPrefix(),describe.get(s));
    }

    Schema.SObjectType sobjectTypeObj = keys.get(recordId.substring(0,3));        
    Schema.DescribeSObjectResult obj = sobjectTypeObj.getDescribe();        
    String query = 'select Id, ';
    for (Schema.ChildRelationship cr: obj.getChildRelationships()){
        if (cr.getRelationshipName() == null){ 
            continue;
        }
        else{
            system.debug('Child Object Relationship Name:'+cr.getRelationshipName());
            query = query + '(select Id from ' + String.valueOf(cr.getRelationshipName()) + '), '; 
        }
    }
    query = query.removeEnd(', ');
    query = query + ' from ' + String.valueOf(sobjectTypeObj) + ' where Id = ' + '\'' + recordId + '\'';
    List<SObject> relatedRecordList = Database.query(query);
}

My problem here is that it is giving me the following error

System.UnexpectedException: SOQL statements cannot query more than 20 different child types.

Is there any way to by pass this governor limit?

Answer 1

This is a documented limit on SOQL parent-child queries:

No more than 20 parent-to-child relationships can be specified in a query.

You'll have to batch your queries in groups of 20 parent-child relationships.

Answer 2

It's governor limit and not possible to by-pass.

But getRelationshipName() returns all the childs including standards ones like

Events,ProcessInstances,Processsteps,Feeds, Topics, RecordActionHistories and list goes on

. Actually you might not need most of them. I would suggest you to review the child which is been received form the getRelationshipName and then include only the necessary ones.

You can also store the necessary child names the static variable or a custom label

and check before adding them to the query.

Hope this helps!!