Hi All,

I am trying to make the record check boxes as checked by default on <lightning:datatable.

please correct me if i am doing wrong in below code

AURA Lightening Component:
<aura:component implements="force:appHostable" access="global" controller="sampleDownload_Class" >
<!-- Handler - Init Method -->
    <aura:handler name="init" value="{!this}" action="{!c.Init}"/>
<aura:attribute name="QuoteIDFromVfPage" type="string" access="global"/>    
    <aura:attribute name="columns" type="List"/>
    <aura:attribute name="data" type="List"/>
    <aura:attribute name="selectedAttachments" type="List"  default="[]"/>
    
<aura:attribute name="preSelectedRows" type="List"/>
<lightning:card title="Generated Documents" >
        <div >
            <lightning:datatable
                                 columns="{! v.columns }"
                                 data="{! v.data}"
                                 keyField="id"                                
                                 onrowselection="{!c.checkboxAttachment}"
                                 selectedRows="{!v.preSelectedRows}"
                                 /> 
        </div>                 
    </lightning:card>  
</aura:component>

Controller JS:

({
    Init : function(component, event, helper) { 
        
        component.set('v.columns', [
            {label: 'Attachment Name', fieldName: 'Name', type: 'text'},
            {label: 'Proposal Name', fieldName: 'parent.name', type: 'text'},
                        
        ]);        
                
        var action = component.get('c.initMethod');
        action.setParams({
            qID : component.get("v.QuoteIDFromVfPage")                        
        });
        action.setCallback(this,function(response){            
            var state = response.getState();
            //alert('successe state is '+state);
            if(state == 'SUCCESS'){
               component.set('v.data', response.getReturnValue());                 
               var selected_rows = helper.getSomeRows(response.getReturnValue(), 3);
               component.set("v.preSelectedRows",selected_rows_mod);
                
            }
        });
        $A.enqueueAction(action);          
     },
})


Apex: Class :::

Public with sharing class sampleDownload_Class {

@AuraEnabled
Public Static List<Attachment> initMethod(String qID){
String currentRecordId = qID;
List<Attachment> attachedFiles = new List<Attachment>();

attachedFiles = [select Id, name, parent.name, parentId from Attachment where parentId =: currentRecordId order By LastModifiedDate DESC limit 50000];
if(attachedFiles.size() > 0)
return attachedFiles;
else
return null;
}
}    

Please help me on this.

Thanks inadvance