ObjectQuery<T>.GroupBy Method (String, String, ObjectParameter[])


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Groups the query results by the specified criteria.

Namespace:   System.Data.Objects
Assembly:  System.Data.Entity (in System.Data.Entity.dll)

public ObjectQuery<DbDataRecord> GroupBy(
	string keys,
	string projection,
	params ObjectParameter[] parameters


Type: System.String

The key columns by which to group the results.

Type: System.String

The list of selected properties that defines the projection.

Type: System.Data.Objects.ObjectParameter[]

Zero or more parameters that are used in this method.

Return Value

Type: System.Data.Objects.ObjectQuery<DbDataRecord>

A new ObjectQuery<T> instance of type DbDataRecord that is equivalent to the original instance with GROUP BY applied.

Exception Condition

The query parameter is null or an empty string.


The projection parameter is null or an empty string.

GroupBy applies the projection specified by the projection parameter. This means that the ObjectQuery<T> returned by the GroupBy method is always of type DbDataRecord. For more information, see Object Queries.

This example is based on the AdventureWorks Sales Model.

This example creates a new ObjectQuery<T> object that contains the results of the existing query grouped by product name.

    using (AdventureWorksEntities context =
        new AdventureWorksEntities())
        string queryString = @"SELECT VALUE product 
            FROM AdventureWorksEntities.Products AS product";

        ObjectQuery<Product> productQuery =
            new ObjectQuery<Product>(queryString,
                context, MergeOption.NoTracking);

        ObjectQuery<DbDataRecord> productQuery2 =
            productQuery.GroupBy("it.name AS pn",
            "Sqlserver.COUNT(it.Name) as count, pn");

        // Iterate through the collection of Products
        // after the GroupBy method was called.
        foreach (DbDataRecord result in productQuery2)
            Console.WriteLine("Name: {0}; Count: {1}",
                result["pn"], result["count"]);

This example returns a set of nested data records that contain the Contact.LastName column, grouped and sorted alphabetically by the first letter of Contact.LastName.

using (AdventureWorksEntities context =
    new AdventureWorksEntities())
    // Define the query with a GROUP BY clause that returns
    // a set of nested LastName records grouped by first letter.
    ObjectQuery<DbDataRecord> query =
        .GroupBy("SUBSTRING(it.LastName, 1, 1) AS ln", "ln")
        .Select("it.ln AS ln, (SELECT c1.LastName " +
        "FROM AdventureWorksEntities.Contacts AS c1 " +
        "WHERE SubString(c1.LastName, 1, 1) = it.ln) AS CONTACT")

    // Execute the query and walk through the nested records.
    foreach (DbDataRecord rec in
        Console.WriteLine("Last names that start with the letter '{0}':",
        List<DbDataRecord> list = rec[1] as List<DbDataRecord>;
        foreach (DbDataRecord r in list)
            for (int i = 0; i < r.FieldCount; i++)
                Console.WriteLine("   {0} ", r[i]);

.NET Framework
Available since 3.5
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