Source: xkcd, via: Pietro.

As we want the callers not to be aware of the way we retrieve data, we have to passing back data to them in the form they expect it: “BusinessEntity” derived classes or collection of them. This may seems hard, but it isn’t. You can build the statement in way that it will produce data in XML, in a format that can be directly deserialized in entity instances.

So, let’s view how we can:

• Compose the SQL statements in such a way the will produce the xml we need
• Deserialize the data from xml to entities

Take a look at this query:

WITH XMLNAMESPACES
(
  'http://www.w3.org/2001/XMLSchema' as xsd
, 'http://www.w3.org/2001/XMLSchema-instance' as xsi
, 'http://schemas.microsoft.com/crm/2006/WebServices' as crm
)
SELECT name as 'crm:name'
     , accountid as 'crm:accountid'
     , donotphonename as 'crm:donotphone/@name'
     , donotphone as 'crm:donotphone'
     , address1_shippingmethodcodename as 'crm:address1_shippingmethodcode/@name'
     , address1_shippingmethodcode as 'crm:address1_shippingmethodcode'
     , modifiedbyname as 'crm:modifiedby/@name'
     , modifiedbydsc as 'crm:modifiedby/@dsc'
     , modifiedby as 'crm:modifiedby'
     , createdbyname as 'crm:createdby/@name'
     , createdbydsc as 'crm:createdby/@dsc'
     , createdby as 'crm:createdby'
     , statuscodename as 'crm:statuscode/@name'
     , statuscode as 'crm:statuscode'
     , statecodename as 'crm:statecode/@formattedValue'
     , statecode as 'crm:statecode'
  FROM Filteredaccount
   FOR XML PATH ('account')

The WITH XMLNAMESPACES, the field aliases and the FOR XML PATH do the magic, and we get data in this format:

<account xmlns:crm="http://schemas.microsoft.com/crm/2006/WebServices" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <crm:name>Adventure Works Ltd.</crm:name>
  <crm:accountid>E85D1177-EE17-DB11-87E4-0000E2998A6B</crm:accountid>
  <crm:modifiedby name="CRM Administrator" dsc="0">89A611D4-C7BD-DB11-A4E3-005056A80A71</crm:modifiedby>
  <crm:createdby name="CRM Administrator" dsc="0">89A611D4-C7BD-DB11-A4E3-005056A80A71</crm:createdby>
  <crm:statuscode name="Active">1</crm:statuscode>
  <crm:statecode formattedValue="Active">Active</crm:statecode>
</account>
<account xmlns:crm="http://schemas.microsoft.com/crm/2006/WebServices" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <crm:name>Contoso Inc.</crm:name>
  <crm:accountid>A00ED7BB-9D0D-DB11-9073-000C293F9D57</crm:accountid>
  <crm:donotphone name="Allow">0</crm:donotphone>
  <crm:modifiedby name="CRM Administrator" dsc="0">89A611D4-C7BD-DB11-A4E3-005056A80A71</crm:modifiedby>
  <crm:createdby name="CRM Administrator" dsc="0">89A611D4-C7BD-DB11-A4E3-005056A80A71</crm:createdby>
  <crm:statuscode name="Active">1</crm:statuscode>
  <crm:statecode formattedValue="Active">Active</crm:statecode>
</account>

That is exactly what you need to obtain, with the help of XmlSerializer, a collection of accounts:

XmlReader xmlReader = cmd.ExecuteXmlReader();
xmlReader.Read();

while (xmlReader.ReadState != ReadState.EndOfFile)
{
    xml = xmlReader.ReadOuterXml();
    StringReader reader = new StringReader(xml);

    account acc = serializer.Deserialize(reader) as account;
    accounts.Add(acc);
}

// convert accounts in a BusinessEntitesCollection...

Note that:
- the standard SQL syntax for a property is:

, property as ‘crm:property‘

- properties expressed by CRM object model in form of “Lookup” are splitted, on the views, in three columns:

, propertyname as ‘crm:property/@name‘
, propertydsc as ‘crm:property/@dsc‘
, property as ‘crm:property‘

- properties expressed by CRM object model in form of “Picklist” and “CrmBoolean” are splitted, on the views, in two columns:

, propertyname as ‘crm:property/@name‘
, property as ‘crm:property‘

- StatusCode and StateCode are the only further singularity.

Given these rules isn’t hard to build a class able to generate statements for any entity type. For an hard-core solution, add something able to translate a QueryExpression in SQL statements…