Select a count of contacts from accounts using FetchXML - dynamics-crm

Question

Does anyone know the FetchXML format in order to select the count of contacts for accounts?
For example, I would have a list of AccountID's that I would us an IN filter for and I would just require the AccountID and the integer count of the contacts for that account.
Solved (see below) with a minor change to group by accounts. Here is the final fetchxml that I used:
<fetch xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" aggregate="true" distinct="false" mapping="logical">
<entity name="contact">
<attribute name="contactid" alias="recordcount" aggregate="count" />
<link-entity name="account" to="accountid" alias="accountid">
<attribute name="accountid" alias="accountid" groupby="true" />
<filter>
<condition attribute="accountid" operator="in">
<value>708039fd-f7b1-e811-a973-000d3af4a510</value>
<value>0a8139fd-f7b1-e811-a973-000d3af4a510</value>
<value>428139fd-f7b1-e811-a973-000d3af4a510</value>
<value>4a8139fd-f7b1-e811-a973-000d3af4a510</value>
<value>618139fd-f7b1-e811-a973-000d3af4a510</value>
<value>9f8139fd-f7b1-e811-a973-000d3af4a510</value>
<value>ae8239fd-f7b1-e811-a973-000d3af4a510</value>
</condition>
</filter>
</link-entity>
</entity>
</fetch>

Answer 1

You can do an aggregate fetch with a group by on the parentcustomerid.
<fetch distinct='false' mapping='logical' aggregate='true'>
<entity name='contact'>
<attribute name='contactid' alias='contact_count' aggregate='countcolumn' />
<attribute name='parentcustomerid' alias='parentcustomerid' groupby='true' />
<link-entity name='account' from='accountid' to='parentcustomerid'>
<filter type='and'>
<condition attribute='accountid' operator='in'>
<value>{00000000-0000-0000-0000-000000000001}</value>
<value>{00000000-0000-0000-0000-000000000002}</value>
</condition >
</filter>
</link-entity>
</entity>
</fetch>

Answer 2

This is straight forward when you use Rollup field.
Then you can query the count easily.
<fetch>
<entity name="account" >
<attribute name="name" />
<attribute name="new_contactcountrollup" />
</entity>
</fetch>
Update:
Why I said subquery is not supported in fetchxml since I was thinking the second solution.
--using just JOIN
SELECT a.accountid, count(1) AS [contact count] FROM contact c
INNER JOIN account a
ON c.parentcustomerid = a.accountid
WHERE a.accountid IN (
'{0ACDC4F5-4885-E811-A967-000D3A1A9407}', '{BA41CEBA-199F-E811-A96B-000D3A1A9EFB}')
GROUP BY a.accountid
--using SUBQUERY
SELECT a.accountid,
(SELECT Count(1) FROM contact c WHERE c.parentcustomerid = a.accountid) AS [contact count]
FROM account a
WHERE a.accountid IN (
'{0ACDC4F5-4885-E811-A967-000D3A1A9407}', '{BA41CEBA-199F-E811-A96B-000D3A1A9EFB}')