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LINQ: Truly language integrated. Using VB functions inside of LINQ Query

By , 12/17/2009 5:15 PM

LINQ is truly integrated into VB.NET. This allows not only to use LINQ-specific query language in a standard VB.NET code, but use VB.NET code in a LINQ query. Consider function from the previous post. To make it universal we can pass one more parameter
“Aggregate Type” and based on that parameter return Min, Max, Avg, Sum or Count

Function GroupBy(ByVal i_sGroupByColumn As String,  ByVal i_sAggregateColumn As String, ByVal i_dSourceTable As DataTable, i_iAggregateType as Integer) As DataTable

     dim aQuery = From row In i_dSourceTable Group By Group1 = row(i_sGroupByColumn) Into Group Select Group1,  Aggr = Choose(i_iAggregateType, Group.Min(Function(row) row(i_sAggregateColumn)), Group.Max(Function(row) row(i_sAggregateColumn)), Group.Sum(Function(row) row(i_sAggregateColumn)), Group.Avg(Function(row) row(i_sAggregateColumn)), Group.Count(Function(row) row(i_sAggregateColumn)))

    return aQuery.toDataTable

End Function

In this example VB.NET function Choose is used inside of a LINQ query’s Select Statement. If i_iAggregateType parameter is equal 1 – Minimum value, will be calculated, 2 – Maximum etc.

Grouping ADO.NET DataTable using LINQ

By , 12/17/2009 10:22 AM

I’ve described before how to group and aggregate data in ADO.NET data table using standard .NET 2.0 features. But if you happen to use .NET 3.5 or above and Visual Studio 2008 or above – that entire block of code can be replaced with a single LINQ query:

Function GroupBy(ByVal i_sGroupByColumn As String,  ByVal i_sAggregateColumn As String, ByVal i_dSourceTable As DataTable) As DataTable

     dim aQuery = From row In i_dSourceTable Group By Group1 = row(i_sGroupByColumn) Into Group Select Group1,  Aggr = Group.Count(Function(row) row(i_sAggregateColumn))

    return aQuery.toDataTable

End Function

The query at line 3 is a LINQ to DataSet query, so reference to System.Data.Linq has to be added to your project. The Group.Count aggregate can be replaced with Group.Max, Group.Min, Group.Sum or Group.Avg to perform respectful function.

There is one caveat though. Continue reading 'Grouping ADO.NET DataTable using LINQ'»

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