UPDATE on CustomField using the SOAP Tooling API

Question

I'm using the SOAP Tooling API to try and update a CustomField (posting to /services/Soap/T/29.0)

The method signature is SaveResult[] update(sObject[] sObjects) - and CustomField extends sObject so it shouldn't be a problem to send that down the wire. However I encounter:

INVALID_TYPE: Must send a concrete entity type.

Then I looked at my raw XML on the wire, I can't say I'm surprised! How is the Tooling API service expected to differentiate between the different supported objects, unless it's doing smarts on the Id?

<?xml version="1.0" encoding="UTF-8"?>
<env:Envelope xmlns:env="http://schemas.xmlsoap.org/soap/envelope/" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <env:Header>
    <SessionHeader xmlns="urn:tooling.soap.sforce.com">
      <sessionId>
        00Db0000000d6mj...ViG5ZyFtqu
      </sessionId>
    </SessionHeader>
  </env:Header>
  <env:Body>
    <update xmlns="urn:tooling.soap.sforce.com">
      <sObjects>
        <Id>00Nb0000007p4tE</Id>
        <DeveloperName>NumberOfLocations</DeveloperName>
        <FullName xsi:nil="true"/>
        <Metadata xsi:nil="true"/>
        <NamespacePrefix xsi:nil="true"/>
        <TableEnumOrId xsi:nil="true"/>
      </sObjects>
    </update>
  </env:Body>
</env:Envelope>

What tag/attribute am I missing that's necessary for it to perceive my CustomField as concrete?

Answer 1

the sObjects element should have an xsi:type attribute, e.g.

<sObjects xsi:type="CustomField">