Retriving Data from CRM

First we need to understand 3 concepts -
1) Query expression
2) QuerybyAttribute
3)FetchXML

Difference between Query Expression and Querybyattribute

The QueryByAttribute class is a less complex class to use than QueryExpression when the query is very simple. It retrieves instances of a specific entity type by specifying a set of attributes and value pairs. Use it to create a query that meets a simple set of criteria, it can have multiple equal conditions that are combined using "AND". Notice that QueryByAttribute does not support "OR". the criteria can be defined using attribute-value pairs. The query returns only those entities meeting all the defined criteria.

QueryExpression provides an object oriented, strongly typed approach to developing queries against the Microsoft Dynamics CRM database. It provides an object oriented model and methods to help create queries. You can also use QueryExpression helper classes and methods for ease.


what is the limitation of query expression - 


3)Fetch Xml- We can have only 10 joins in this.