Episode 12:Relationship Queries in Apex -Salesforce

In this blog, we will deep dive into the concept of relationship queries. So Before wasting any time, let's let started.😊

Most of the time we need to query the data from more than one standard or custom object at a time i.e we need to traverse either from parent to child or from child to parent objects. SOQL (Salesforce Object Query Language) provides us the syntax to write these queries which are called the  Relationship Queries. We can visualize the Relationship Queries same as Joins in SQL.

Note: If you are using multiple objects in the same query to fetch the data, always remember those objects must be related to each other i.e there must be a parent -to- child or child-to-parent relationships between those objects.

Parent to Child Relationship Query

We use this query when we are referring to child object records from the parent object. Here, the main object for the query is the parent object.

Standard Object Relationship 

Let's take an example of the Account and Contact object where Account is the parent of Contact Object.

In order to traverse parent-to- child or child-to-parent relationship, relationship name is given to each relationship.

Now the question arises how can we find the relationship name between two objects.

Do not worry!It is very simple.In this case you have to find the relationship name between Account and Contact, so first open the lookup relationship field present on contact child object i.e Account Name.

Drill down on the Account Name and below screen will appears and here you can find the child relationship name which is contacts in this case.

Now once we have found out the relationship name we can write the query:

Select Name,Id,Industry,Rating ,(select Name,Phone,Email from Contacts) from Account limit 10

The above query will give below results i.e list of contacts for the given Account.

Note: Child Relationship Name in Parent-to-child relationship is always the plural of the child object name.

Custom Objects Relationship 

For Example, there are two custom objects one is  Company__c and another one is Employee__c.

One Company can have multiple employees so they share one -to -many lookup relationships where the company is the parent object and the employee is the child object. 

Now If you want to reach the employee object record from the company object, you have to write your query on the parent object (Company__c in this case)and fetch the related child records( employees).

Before writing this query we need the relationship name between those objects. Here the relationship name is employees__r.

Query Syntax :

 Select Id,Name ,(select Id,Name,Company__c from Employees__r) from Company__c

Note: When you are travesing  from parent to child in Custom Objects Relationship, then use

 plural of the child object name( without the __c)  and append an  __r .

NOTE: Only 1 Level of the nested query is allowed(  you can remember as 1 LEVEL DOWN)

Child to Parent Relationship Query

We use this query when we are referring to Parent object records from the Child object. Here, the main object for the query is the Child object.

Standard Object Relationship 

Before jumping directly to query we need to know something.Yes , you are right we need the relationship Name between two standard objects.

Lets again take the example of Account and Contact Object where Account is the parent of the Contact Object and the value of relationship name in contact is Account and you can traverse the relationship by specifying the parent using dot notation.

For Example,

SELECT Id, Account.Name, Account.Industry, Account.Rating  FROM Contact limit 10

The above query will give below results:

Custom Objects Relationship 

When you use a child-to-parent relationship, you can use dot notation with the relationship name as given below:

select id, name,company__c,company__r.name from employee__c limit 10

NOTE: You can Access up to 5 levels of parents using DOT Notation( i.e 5 LEVEL UP)

Thanks for reading my blog.Stay tuned till then keep learning and keep sharing.