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parent to child soqls

Parent to Child SOQl

If two objects are connected by relationship field like (master detail or lookup relation ) then we can write a soql to fetch child records from parent object

Ex: Account and contact object are connected by using lookup relation

Ex: Customer object and Transaction object are connected by using master-detail relation

Example Program to display Account records along with corresponding contact records

public  class ParentChild {

     public List<Account> accs{set;get;}

     public List<Customer__c> cust{set;get;}

     public ParentChild(){

accs=[select Name,Industry,(select id,lastname,firstname from Contacts)

        from Account];

cust=[select Customer_Name__c,AType__c ,(select Type__c,Amount__c from

                  Transactions__r) from Customer__c];

         

     }

}

VF page :

<apex:page controller="ParentChild">

     <apex:pageBlock title="Account and Contacts">

          <apex:pageBlockTable value="{!accs}" var="a">

              <apex:column value="{!a.Name}" />

              <apex:column value="{!a.industry}" />

              <apex:column headerValue="Contacts">

                   <apex:repeat value="{!a.contacts}" var="b">

                        {!b.lastname} -{!b.firstname}<br/>

                   </apex:repeat>

              </apex:column>

          </apex:pageBlockTable>

 </apex:pageBlock>

 <apex:pageBlock title="Customers and Transactions">

          <apex:pageBlockTable value="{!cust}" var="a">

              <apex:column value="{!a.Customer_Name__c}" />

              <apex:column value="{!a.AType__c}" />

              <apex:column headerValue="Transactions">

                   <apex:repeat value="{!a.Transactions__r}" var="b">

                        {!b.Type__c} -{!b.amount__c}<br/>

                   </apex:repeat>

              </apex:column>

          </apex:pageBlockTable>

 </apex:pageBlock>

</apex:page>