How to use JavaScript to fill parent lookup on form in Dynamics 365 CRM on-premise?

Lets assume that I have 3 related Entities (PhoneCall-Account-Contact). For detailed information I must say in phonecall form I have a custom lookup field that related to account and another one that related to contact and last one again related to account which used for parent account. Now I want a solution that help me when I fill account field after that fill parent account lookup with correct data or if I fill contact lookup first of all fill account with correct data then fill parent account field with correct data. I search many ways but I couldn’t find any way to find correct parent account and fill my lookups even I use business rules but it can’t help me.

Now I have seen on many websites that CRM REST BUILDER was suggested. I had Used it but it couldn’t solve my problem.

Answer

What you need is, a Javascript function to trigger on change of first lookup to query necessary fields from parent record and fill it in current child record form. Read more

function fillParentAccount() {

var lookup= Xrm.Page.getAttribute("accountfieldname").getValue();  //you will get the id with exxtra double quotes or square brackets by doing get value hence you to make it readable by CRM , you must slice it. i have use the below method:
var newid = lookup[0].id.slice(1, -1);  // you will get perfect id like "EDCJDKDJDKJDJDKJDJKD" here.
var req = new XMLHttpRequest(); //once you have the id , you have frame to make a webapi GET call by proving the newid we got.

req.open("GET", Xrm.Page.context.getClientUrl() + "/api/data/v8.1/accounts(" + newid + ")?$select=_parentaccountfieldname_value", true);
req.setRequestHeader("OData-MaxVersion", "4.0");
req.setRequestHeader("OData-Version", "4.0");
req.setRequestHeader("Accept", "application/json");
req.setRequestHeader("Content-Type", "application/json; charset=utf-8");
req.setRequestHeader("Prefer", "odata.include-annotations="*"");
req.onreadystatechange = function () {
if (this.readyState === 4) {
req.onreadystatechange = null;
if (this.status === 200) {
var result = JSON.parse(this.response); // you will get the retrieved value in object we stored in result var.
var retrivedvalue= result._parentaccountfieldname_value; //get the id of the field
var retrivedformatedvalue= result["[email protected]edValue"]; //get the formatted name of the field
if (retrivedvalue!= null) {
var value = new Array();
value[0] = new Object();
value[0].id = retrivedvalue;
value[0].name = retrivedformatedvalue;
value[0].entityType = "account";
Xrm.Page.getAttribute("parentaccountfield").setValue(value); //set the lookup value finally
}
else
alert("some textt!!!!!!") // optional
} else {
Xrm.Utility.alertDialog(this.statusText);
}
}
};
req.send();

Make sure to change the field names and accuracy of your customizations.