How can I dynamically select my Table at runtime with Dynamic LINQ

Question

I\'m developing an application to allow engineers to conduct simple single table/view queries against our databases by selecting Database, Table, Fields.

I get how t

Answer 1

You can use GetTable() to get the corresponding ITable of your data. Then coupled with using DLINQ, making it relatively easy.

This example uses the AdventureWorks database. My project has the context defined in the DatabaseTest assembly in the DatabaseTest.AdventureWorks namespace.

'' need my database and DLINQ extensions up top
Imports DatabaseTest.AdventureWorks
Imports System.Linq.Dynamic

'' sample inputs
Dim dc = New AdventureWorksDataContext()
Dim tableName = "Contact"
Dim whereClauses() = {"FirstName = ""John"" OR LastName = ""Smith"""}
Dim selectColumns() = {"FirstName", "LastName"}

'' get the table from a type (which corresponds to a table in your database)
Dim typeName = "DatabaseTest.AdventureWorks." & tableName & ", DatabaseTest"
Dim entityType = Type.GetType(typeName)
Dim table = dc.GetTable(entityType)
Dim query As IQueryable = table

'' add where clauses from a list of them
For Each whereClause As String In whereClauses
    query = query.Where(whereClause)
Next

'' generate the select clause from a list of columns
query = query.Select(String.Format("new({0})", String.Join(",", selectColumns)))

In retrospect, using reflection might have been the easier way to get the table since you have the name already. But then the names might not have a 1-to-1 correspondence so you'll have to compensate for it.

Dim table As ITable = dc.GetType().GetProperty(tableName & "s").GetValue(dc, Nothing)

Answer 2

See Get table-data from table-name in LINQ DataContext.

This is probably actually better done by using direct SQL statements. LINQ will just get in your way.

VB Conversion:

NotInheritable Class DataContextExtensions
    Private Sub New()
    End Sub
    <System.Runtime.CompilerServices.Extension> _
    Public Shared Function GetTableByName(context As DataContext, tableName As String) As ITable
        If context Is Nothing Then
            Throw New ArgumentNullException("context")
        End If
            If tableName Is Nothing Then
                Throw New ArgumentNullException("tableName")
            End If
        Return DirectCast(context.[GetType]().GetProperty(tableName).GetValue(context, Nothing), ITable)
    End Function
End Class

Usage:

Dim myDataContext as New MyCustomDataContext
myDataContext.GetTableByName("ORDERS").Where("...")