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I've recently discovered that the Lists.asmx ignores your attempts to reset a field's value to empty string or null with Lists.UpdateListItems. Not a very well documented limitation discovered by trial and error.

Can someone advise on the possibility to reset field values using FP RPC / OWSAPI from AJAXy pages? Or am I missing something in the OOTB web service functionality / CAML syntax? I mean without deploying a custom Web Service just for that little generic task?

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What have you tried (just so I don't go and try the exact same things)? – Marc D Anderson May 20 '10 at 17:46
I tried <Field></Field> and for lookups <Field>0;#</Field> and <Field>;#</Field>. To no avail. Both via AJAX calls and via u2u CAML Query Builder. I'm now looking into owsvsvr.dll calls which may be what DataView WebPart and SPD do. – Alexey Krasheninnikov May 20 '10 at 19:40
Have you tried using a variable set to null or empty? – spevilgenius May 22 '10 at 20:19
Where exactly? I'm not aware of a way to reference null-valued client side variables via SOAP XML-based request other than just <Field Name='' /> – Alexey Krasheninnikov May 23 '10 at 23:45
Well I think I'd like to revive this discussion. Let's start a bounty. – Alexey Krasheninnikov Jun 27 '11 at 14:27
up vote 4 down vote accepted

I just did a test with SPServices where I set a Single line of text column to an empty string (""), which seemed to work just fine. This was with WSS 3.0 (the simplest test case, IMO).

    operation: "UpdateListItems",
    async: false,
    listName: "Sales Opportunities",
    ID: 5,
    valuepairs: [["StateID", ""]],
    completefunc: function (xData, Status) {

This generates the call:

<soap:Envelope xmlns:xsi="" xmlns:xsd="" xmlns:soap="">
    <UpdateListItems xmlns="">
      <listName>Sales Opportunities</listName>
        <Batch OnError="Continue">
          <Method ID="1" Cmd="Update">
            <Field Name="StateID"></Field>
            <Field Name="ID">5</Field>


I just did the same thing for a Lookup column and a Person or Group column. The valuepairs line is:

valuepairs: [["State", ""], ["Sales_x0020_Rep", ""]],

Both columns were "emptied".

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OK, how about a lookup field? – Alexey Krasheninnikov Jun 27 '11 at 20:16
+1, just sending <Field Name="LookupField"></Field> seems to work fine. – Kit Menke Jun 28 '11 at 14:33
Yay! I got 50 points. I'll go buy something with them right away. ;+) – Marc D Anderson Jun 29 '11 at 16:36

In the end, had to resort to writing a custom web service that also makes great bandwidth savings.

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But that's not the definitive answer to my own inquiry whether or not there IS a way to reset a field value to null. – Alexey Krasheninnikov Jun 27 '11 at 14:28

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