Lightning:datatable preselect rows

Question

I have a lightning datatable that i would like to preselect all the rows when i load it. I'm currently doing like described in the lighting:datatable definition page but no luck so far

Supposedely this line is preselecting all rows as the selectedRows from datatable is binded to the attribute

component.set('v.selectedRows', selected);

FullCode:

.component

<aura:attribute name="selectedRows" type="List"/>

<lightning:datatable aura:id="partnerTable" data="{!v.partnerdata }" 
columns="{!v.partnercolumns}" keyField="Id" selectedRows="
{!v.selectedRows}"/>

.controller

searchPartners : function(component, event, helper) {
  helper.searchPartners(component, event, helper);},

.helper

searchPartners : function(component, event, helper) {
    var selectedProducts = component.get("v.selectedProducts");
    var action = component.get("c.getAccountData");
    action.setParams({
        "products": selectedProducts
    });
    var accs=[];
    var selected=[];
    action.setCallback(this, function(response) { 
        var state = response.getState();
        if (state === "SUCCESS") {
            var accounts = response.getReturnValue();
            accounts.forEach(function(account) {
                accs.push({name: account.Name, id: account.Id});
                selected.push(account.Id);
            });  
            component.set('v.partnercolumns', [                
                {label: 'Name', fieldName: 'name', type: 'text'}
            ]); 
            component.set('v.partnerdata', accs);
            component.set('v.selectedRows', selected);  
        }
        else {
            console.log("Failed with state: " + state);
        }              
    });
    $A.enqueueAction(action);         
},   

Answer 1

It's possible to preselect items, however I noticed a bug on API v42 (current version) and I confirmed that with SFDC support team. When using the attribute to bind the selected rows, it simply doesn't work, however if you find the lightning:datatable and then change the selectedRows, it works properly.

    component = component.find("partnerTable");
    component.set("v.selectedRows", selectedRowsIds);

Please find an example below, I'm creating a mockdata and selecting the first item by the Id.

Component

    <aura:attribute name="partnerdata" type="Object" access="private" />
    <aura:attribute name="partnercolumns" type="List" access="private" />
    <aura:attribute name="partnerSelectedRows" type="List" access="private" default="" />

    <!--
    <lightning:datatable aura:id="partnerTable" data="{!v.partnerdata}" 
    columns="{!v.partnercolumns}" keyField="Id" selectedRows="{!v.partnerSelectedRows}"/>
    -->

    <lightning:datatable aura:id="partnerTable" data="{!v.partnerdata}" 
    columns="{!v.partnercolumns}" keyField="Id" /> 

Controller

({
    doInit : function(component, event, helper) {
        helper.getMockData(component, event, helper);
    }
})

Helper

({
    getMockData: function(component, event) {
        console.log("Load mock data!");
        component.set("v.partnercolumns", [{
                label: "Name",
                fieldName: "Name",
                type: "text"
            },
            {
                label: "Status",
                fieldName: "status__c",
                type: "text"
            },
            {
                label: "Created Date",
                fieldName: "createdate__c",
                type: "date"
            }
        ]);
        component.set("v.partnerdata", [{
                Id: "a0319000001GtsjAAC",
                Name: "John Doe",
                status__c: "Active",
                createdate__c: "2005-01-01"
            },
            {
                Id: "a0319000001GtsjAAD",
                Name: "Mary Doe",
                status__c: "Active",
                createdate__c: "2005-02-10"
            }
        ]);

        var selectedRowsIds = ["a0319000001GtsjAAC"];

        // I was expecting the line to work
        //component.set("v.partnerSelectedRows", selectedRowsIds);

        // Workaround to selectRows
        component = component.find("partnerTable");
        component.set("v.selectedRows", selectedRowsIds);

    }
})