$webwork.htmlEncode($page.space.name) : Feature Locking
This page last changed on Nov 21, 2005 by cholmes.

Summary

A WFS has the ability to lock features to prevent more than one person from updating the feature at one time.

Here's a set of possible actions that might occur if Person A and Person B are editing a dataset using a WFS:

1. Person A grabs a lock on a set of feature - "Delaware" and "Idaho"
2. If Person B tries to grab a lock on either of these features, an error will occur
3. If Person B tries to update these features, an error will occur
4. Person A can update the features and release the lock
5. Now, Person B can lock (and update) the features

Details

The WFS locking scheme is very simple, but there are several subtle issue involving when the locks are released:

1. Whenever you do a transaction on a locked feature, it becomes unlocked

2. If you set releaseAction="ALL" (the default), then ALL features associated with that lockID will be released after the transaction

3. If you set releaseAction="SOME", then only the features you touched during the transaction will be released, the others will remain locked

4. If you mention a LockID in your transaction, then you must have a lock on all the features touched by that transaction or you'll get an error. This causes people a lot of problems.

These are described in more detail below.

Examples (Using default Geoserver Install)

NOTE: You will get a different LockID than I do when you run these commands. Please replace the LockID in these transactions with the one the server returns to you.

Get a lock on "Delaware" and "Idaho"

<wfs:GetFeatureWithLock service="WFS" version="1.0.0"
  outputFormat="GML2"
  xmlns:topp="http://www.openplans.org/topp"
  xmlns:wfs="http://www.opengis.net/wfs"
  xmlns:ogc="http://www.opengis.net/ogc"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://www.opengis.net/wfs
                      http://schemas.opengis.net/wfs/1.0.0/WFS-basic.xsd">
  <Query typeName="topp:states">
  <Filter>
  	<Or>
    		<PropertyIsEqualTo>
                	<PropertyName>STATE_NAME</PropertyName>
                	<Literal>Delaware</Literal>
          	</PropertyIsEqualTo>
          	<PropertyIsEqualTo>
		        <PropertyName>STATE_NAME</PropertyName>
		        <Literal>Idaho</Literal>
          	</PropertyIsEqualTo>
        </Or>
   </Filter>
  </Query>
</wfs:GetFeatureWithLock>

NOTE: you will get a lockID back from this response (its right at the top in the "<wfs:FeatureCollection>" element. Remember this.

Try to update the feature. This will fail because you do not own the lock.

<wfs:Transaction service="WFS" version="1.0.0"
  xmlns:topp="http://www.openplans.org/topp"
  xmlns:ogc="http://www.opengis.net/ogc"
  xmlns:wfs="http://www.opengis.net/wfs">
  <wfs:Update typeName="topp:states">
    <wfs:Property>
      <wfs:Name>MALE</wfs:Name>
      <wfs:Value>-999999</wfs:Value>
    </wfs:Property>
    <ogc:Filter>
      <PropertyIsEqualTo>
                      	<PropertyName>STATE_NAME</PropertyName>
                      	<Literal>Delaware</Literal>
          	</PropertyIsEqualTo>
    </ogc:Filter>
  </wfs:Update>
</wfs:Transaction>

This time mention the lockId you got from above (replace with what you got)

NOTE: in this case we did not specify a releaseAction, so it defaults to "ALL". In this case, both locks are released.

<wfs:Transaction service="WFS" version="1.0.0"
   xmlns:topp="http://www.openplans.org/topp"
   xmlns:ogc="http://www.opengis.net/ogc"
   xmlns:wfs="http://www.opengis.net/wfs">
   <wfs:LockId>GeoServer_4d1d517227455c58</wfs:LockId>
   <wfs:Update typeName="topp:states">
     <wfs:Property>
       <wfs:Name>MALE</wfs:Name>
       <wfs:Value>-999999</wfs:Value>
     </wfs:Property>
     <ogc:Filter>
       <PropertyIsEqualTo>
                       	<PropertyName>STATE_NAME</PropertyName>
                       	<Literal>Delaware</Literal>
           	</PropertyIsEqualTo>
     </ogc:Filter>
   </wfs:Update>
</wfs:Transaction>

This transaction will fail because the lock has been released by the previous transaction.

NOTE: even though the row is no longer locked, because you mention a lockid the row must be locked.

<wfs:Transaction service="WFS" version="1.0.0"
   xmlns:topp="http://www.openplans.org/topp"
   xmlns:ogc="http://www.opengis.net/ogc"
   xmlns:wfs="http://www.opengis.net/wfs">
   <wfs:LockId>GeoServer_4d1d517227455c58</wfs:LockId>
   <wfs:Update typeName="topp:states">
     <wfs:Property>
       <wfs:Name>MALE</wfs:Name>
       <wfs:Value>-1234</wfs:Value>
     </wfs:Property>
     <ogc:Filter>
       <PropertyIsEqualTo>
                       	<PropertyName>STATE_NAME</PropertyName>
                       	<Literal>Delaware</Literal>
           	</PropertyIsEqualTo>
     </ogc:Filter>
   </wfs:Update>
</wfs:Transaction>

This transaction works because the row is not locked and you have not mentioned a lockid.

<wfs:Transaction service="WFS" version="1.0.0"
   xmlns:topp="http://www.openplans.org/topp"
   xmlns:ogc="http://www.opengis.net/ogc"
   xmlns:wfs="http://www.opengis.net/wfs">
   <wfs:Update typeName="topp:states">
     <wfs:Property>
       <wfs:Name>MALE</wfs:Name>
       <wfs:Value>-7890</wfs:Value>
     </wfs:Property>
     <ogc:Filter>
       <PropertyIsEqualTo>
                       	<PropertyName>STATE_NAME</PropertyName>
                       	<Literal>Delaware</Literal>
           	</PropertyIsEqualTo>
     </ogc:Filter>
   </wfs:Update>
</wfs:Transaction>

Please re-execute the GetFeatureWithLock and get the two rows locked.

NOTE: this time we set the releaseAction to "SOME". At the end of this transaction, the Delaware lock is released, but the Idaho lock remains.

<wfs:Transaction service="WFS" version="1.0.0"
    xmlns:topp="http://www.openplans.org/topp"
    xmlns:ogc="http://www.opengis.net/ogc"
    xmlns:wfs="http://www.opengis.net/wfs"
    releaseAction="SOME">
    <wfs:LockId>GeoServer_6de22372276223da</wfs:LockId>
    <wfs:Update typeName="topp:states">
      <wfs:Property>
        <wfs:Name>MALE</wfs:Name>
        <wfs:Value>-999999</wfs:Value>
      </wfs:Property>
      <ogc:Filter>
        <PropertyIsEqualTo>
                        	<PropertyName>STATE_NAME</PropertyName>
                        	<Literal>Delaware</Literal>
            	</PropertyIsEqualTo>
      </ogc:Filter>
    </wfs:Update>
</wfs:Transaction>

LockFeature Examples

An alternative way of locking a feature is to use LockFeature. Its almost exactly the same as GetFeatureWithLock, but it doesnt return the actual features. For example,

<wfs:LockFeature service="WFS" version="1.0.0"
  outputFormat="GML2"
  xmlns:topp="http://www.openplans.org/topp"
  xmlns:wfs="http://www.opengis.net/wfs"
  xmlns:ogc="http://www.opengis.net/ogc"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://www.opengis.net/wfs
                      http://schemas.opengis.net/wfs/1.0.0/WFS-basic.xsd">
  <Lock typeName="topp:states">
  <Filter>
  	<Or>
    		<PropertyIsEqualTo>
                	<PropertyName>STATE_NAME</PropertyName>
                	<Literal>Delaware</Literal>
          	</PropertyIsEqualTo>
          	<PropertyIsEqualTo>
		        <PropertyName>STATE_NAME</PropertyName>
		        <Literal>Idaho</Literal>
          	</PropertyIsEqualTo>
        </Or>
   </Filter>
  </Lock>
</wfs:LockFeature>

returns:

<?xml version="1.0" encoding="UTF-8"?>

<WFS_LockFeatureResponse xmlns="http://www.opengis.net/wfs" 
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
xsi:schemaLocation="http://www.opengis.net/wfs 
http://localhost:8080/geoserver/data/capabilities/wfs/1.0.0/WFS-transaction.xsd">

<LockId>GeoServer_218172b636a740c3</LockId>

</WFS_LockFeatureResponse>

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Document generated by Confluence on Jan 16, 2008 23:28