Executing large FetchXML with WebAPI

You can easily execute fetchxml in WebAPI using the “fetchXml” query parameter. But this “GET” method won’t work, if the fetchxml is too big. In this case, you have to use the “POST” method to execute the fetchxml.

Sample Request Header:

Accept: application/json
OData-MaxVersion: 4.0
OData-Version: 4.0
Content-Type: multipart/mixed;boundary=batch_contactfetch

Sample Request Body:

--batch_contactfetch
Content-Type: application/http
Content-Transfer-Encoding: binary

GET https://[CRM URL]/api/data/v8.2/contacts?fetchXml=<fetch count="10" ><entity name="contact" ><attribute name="fullname" /></entity></fetch> HTTP/1.1
Content-Type: application/json
OData-Version: 4.0
OData-MaxVersion: 4.0

--batch_contactfetch--

Sample Code:

var req = new XMLHttpRequest();
req.open("POST", Xrm.Page.context.getClientUrl() + "/api/data/v8.2/$batch", true);
req.setRequestHeader("OData-MaxVersion", "4.0");
req.setRequestHeader("OData-Version", "4.0");
req.setRequestHeader("Accept", "application/json");
req.setRequestHeader("Content-Type", "multipart/mixed;boundary=batch_contactfetch");
req.onreadystatechange = function() {
    if (this.readyState === 4) {
        req.onreadystatechange = null;
        if (this.status === 200) {
            var response = JSON.parse(this.response.substring(this.response.indexOf('{'),this.response.lastIndexOf('}')+1));
			console.log(response.value);
        } else {
            Xrm.Utility.alertDialog(this.statusText);
        }
    }
};

var body = '--batch_contactfetch\n'
body += 'Content-Type: application/http\n'
body += 'Content-Transfer-Encoding: binary\n'
body += '\n'
body += 'GET ' + Xrm.Page.context.getClientUrl()+'/api/data/v8.2/contacts?fetchXml=<fetch count="10" ><entity name="contact" ><attribute name="fullname" /></entity></fetch> HTTP/1.1\n'
body += 'Content-Type: application/json\n'
body += 'OData-Version: 4.0\n'
body += 'OData-MaxVersion: 4.0\n'
body += '\n'
body += '--batch_contactfetch--'

req.send(body);

Request Screenshot

Response Screenshot