Build queries with QueryExpression || Use the QueryExpression class in Dynamics 365

Build queries with QueryExpression:

1. A query expression is used for single-object searches. For example, you can create a search to return all accounts that match certain search criteria. 

2. The QueryBase class is the base class for query expressions. There are three derived classes: QueryExpression, QueryByAttribute, and FetchExpression. 

• The QueryExpression the class supports complex queries. 
• The QueryByAttribute class is a simple means to search for entities where attributes match specified values.
• The third derived class, FetchExpression is used with FetchXML, the proprietary Dataverse query language, can be used to perform some queries by using XML-based queries.

Query expressions are used in methods that retrieve more than one record, such as the IOrganizationService.RetrieveMultiple method.

Let's start with an example How to use queryExpression class.

Use the QueryExpression class

//  Query using ConditionExpression and FilterExpression 
ConditionExpression condition1 = new ConditionExpression();
condition1.AttributeName = "lastname";
condition1.Operator = ConditionOperator.Equal;
condition1.Values.Add("White");
 
FilterExpression filter1 = new FilterExpression();
filter1.Conditions.Add(condition1);
 
QueryExpression query = new QueryExpression("contact");
query.ColumnSet.AddColumns("firstname", "lastname");
query.Criteria.AddFilter(filter1);
 
EntityCollection result1 = _serviceProxy.RetrieveMultiple(query);
Console.WriteLine(); Console.WriteLine("Query using Query Expression with ConditionExpression and FilterExpression");
Console.WriteLine("---------------------------------------");
foreach(var a in result1.Entities)
{
    Console.WriteLine("Name: " + a.Attributes["firstname"] + " " + a.Attributes["lastname"]);
}

Console.WriteLine("---------------------------------------");

Use the FilterExpression class

In Microsoft Dataverse, you can use the FilterExpression class to build a query that expresses multiple conditions. For example, you can create a query expression that is the equivalent of a SQL statement such as ([FirstName] = 'Mike' OR [FirstName] = 'Zen') AND [City] = 'Pune'.

The below example shows how to use the FilterExpression class.

QueryExpression query = new QueryExpression("contact");

query.ColumnSet.AddColumns("firstname", "lastname", "address1_city");

 

query.Criteria = new FilterExpression();

query.Criteria.AddCondition("address1_city", ConditionOperator.Equal, "Pune");

 

FilterExpression childFilter = query.Criteria.AddFilter(LogicalOperator.Or);

childFilter.AddCondition("lastname", ConditionOperator.Equal, "John");

childFilter.AddCondition("lastname", ConditionOperator.Equal, "White");

 

// Pass query to service proxy  

EntityCollection results = _serviceProxy.RetrieveMultiple(query);

Console.WriteLine();

Console.WriteLine("Query using QE with multiple conditions and filters");

Console.WriteLine("---------------------------------------");

 

// Print results  

foreach(var a in results.Entities)

{

    Console.WriteLine("Name: {0} {1}", a.GetAttributeValue<string>("firstname"), a.GetAttributeValue<string>("lastname"));

    Console.WriteLine("City: {0}", a.GetAttributeValue<string>("address1_city"));

}

Console.WriteLine("---------------------------------------");

References: MS Docs

Thanks!!!
Happy Learning ...