LINQ to CRM - OR in Where clause

问题

I am trying to bring some data from Dynamics CRM 2011 using LINQ. The goal is to bring all Contact records that have changes since certain date OR have a child entity (PERC files) changed since that same date. The query looks like that:

// Bring all students who have changes (at Contact entity) after specific date
// momentInTime or the status of any of their perc files has been changed since
// that date 
var students = (from c in ContactSet
                join pl in cga_portallogonSet on c.Id equals pl.cga_ContactId.Id
                join ef in cga_percfileSet on c.Id equals ef.cga_StudentId.Id
                where
                    (pl.cga_PortalLogonRole.Value == 284970000) // student
                where
                    (c.ModifiedOn >= momentInTime || c.CreatedOn > momentInTime)
                    ||
                    (ef.cga_statuschangedate >= momentInTime)
                select c.cga_StudentNumber).Distinct().ToList();

This produces the following error message:

'Contact' entity doesn't contain attribute with Name = 'cga_statuschangedate'.

I cannot figure out how to do OR on two different entities. The MSDN says you need WHERE clause for each entity:

where Clause

In order to filter the result set, where clauses can be added against one or more of the >entities. Each where clause may only contain conditions against an individual entity type. >A composite condition involving multiple entities is not valid. Instead, each entity >should be filtered in separate where clauses.

http://msdn.microsoft.com/en-us/library/ff681565.aspx

Is there another way of achieving what I need?

回答1:

Unfortunately you cannot achieve what you want in a single linq statement beacuse the liunq provider they use boils down to fetchXML, and fetchXML does not support the scenario you are using.

More detail... Fetch gives you condition's inside of entity's or link-entity's. These condition elements cannot have attributes in them from other linked entities, only the direct parent entity or link-entity. Here is one of many microsoft forum posts referencing this limitation of fetchXML

Probably not the answer you were looking for, eh? As an ugly alternative you you can run two separate queries and filter in memory (as damaging as that may be to performance). Or better yet if you are an on-premise deployment you can write some sql against the filtered views. Good luck.

来源：https://stackoverflow.com/questions/10422514/linq-to-crm-or-in-where-clause