How to use variables in dot notation to find child relationship name?

Question

Instead of teacher__c and student__c, they needs be dynamic variables. How can I substitute these API names with variables: parentApiName and childApiName?

for (ChildRelationship relation : SObjectType.teacher__c.getChildRelationships())
    if (relation.getChildSObject() == student__c.sObjectType)
        system.debug(relation.getRelationshipName());

What I tried and failed:

for (ChildRelationship relation : SObjectType.${parentApiName}.getChildRelationships())
    if (relation.getChildSObject() == `${childApiName}.sObjectType`)
        system.debug(relation.getRelationshipName());

Answer 1

You can get Schema information dynamically by leveraging some of the dynamic Schema methods like describeSObjects which takes a list of strings. I've taken your code and written a method that accepts the parent type and child type dynamically and returns the relationship name, if one exists.

public static String getRelationshipName(String parentObjectApiNames, String childObjectApiName)
    List<Schema.DescribeSObjectResult> result = Schema.describeSObjects(new List<String>{parentObjectApiNames});

    for (ChildRelationship relation : result[0].getChildRelationships()) {
        if (relation.getChildSObject().getDescribe().getName() == childObjectApiName) {
            return relation.getRelationshipName();
        }
    }

    return null;
}