Dynamics CRM中构建查询

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<fetch version="1.0" output-format="xml-platform" mapping="logical" distinct="true">  <entity name="lead">    <attribute name="fullname" />    <link-entity name="task" from="regardingobjectid" to="leadid" alias="ab" link-type="outer">       <attribute name="regardingobjectid" />    </link-entity>    <filter type="and">        <condition entityname="ab" attribute="regardingobjectid" operator="null" />    </filter>  </entity><fetch/>

QueryExpression qx = new QueryExpression("lead");qx.ColumnSet.AddColumn("subject");LinkEntity link = qx.AddLink("task", "leadid", "regardingobjectid", JoinOperator.LeftOuter);link.Columns.AddColumn("subject");link.EntityAlias = "tsk";qx.Criteria = new FilterExpression();qx.Criteria.AddCondition("tsk", "activityid", ConditionOperator.Null);

等效于以下SQL

SELECT lead.FullName FROMLeads as leadLEFT OUTER JOIN Tasks as abON (lead.leadId = ab.RegardingObjectId)WHERE ab.RegardingObjectId is null

fetchXML与QueryExpression的link-entity正好相反

LINQ也可以构建查询

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