如何返回LINQ实体的列名

Question

I am using LINQ to SQL queries to return data in my application. However I find it is now needful for me to return the column Names. Try as I might I have been completely unable to find out how to do this on the internet.

So if my LINQ entity table has the properties (Last_Name, First_name, Middle_Name) I need to return:

Last_name
First_Name
Middle_name

rather than the usual

Smith
John
Joe

Answer 1

Lets assume you're talking about the Contact Table in the assembly named YourAssembly in a Context called MyDataContext

Using Reflection against a Table

You can use reflection to get the properties like you would any type

var properties = from property in Type.GetType("YourAssembly.Contact").GetProperties() select property.Name ;

  foreach (var property in properties) Console.WriteLine(property); 

As shaunmartin notes this will return all properties not just Column Mapped ones. It should also be noted that this will return Public properties only. You'd need to include a BindingFlags value for the bindingAttr Parameter of GetProperties to get non-public properties

Using the Meta Model

You can use the Meta Model System.Data.Linq.Mapping to get the fields ( I added IsPersistant to only get the Column Mapped properties)

        AttributeMappingSource mappping = new System.Data.Linq.Mapping.AttributeMappingSource();
        var model = mappping.GetModel(typeof (MyDataContext));
        var table = model.GetTable(typeof (Contact));

        var qFields= from fields in table.RowType.DataMembers
                where fields.IsPersistent == true
                select fields;

        foreach (var field in qFields)
            Console.WriteLine(field.Name);

Using Reflection from a query result

If on the other hand you wanted it from a query result you can still use reflection.

        MyDataContextdc = new MyDataContext();
        Table<Contact> contacts = dc.GetTable<Contact>();
        var q = from c in contacts
                select new
                {
                    c.FirstName,
                    c.LastName
                };


        var columns = q.First();
        var properties = (from property in columns.GetType().GetProperties()
                        select property.Name).ToList();

Answer 2

You could certainly do it with some LINQ-To-Xml directly against the ".edmx" file or the embedded model resources in the compiled assembly.

The below query gets the field (not column) names. If you need the columns then just change the query to suit.

var edmxNS = XNamespace.Get(@"http://schemas.microsoft.com/ado/2007/06/edmx");
var schemaNS = XNamespace.Get(@"http://schemas.microsoft.com/ado/2006/04/edm");

var xd = XDocument.Load(@"{path}\Model.edmx");

var fields =
    from e in xd
        .Elements(edmxNS + "Edmx")
        .Elements(edmxNS + "Runtime")
        .Elements(edmxNS + "ConceptualModels")
        .Elements(schemaNS + "Schema")
        .Elements(schemaNS + "EntityType")
    from p in e
        .Elements(schemaNS + "Property")
    select new
    {
        Entity = e.Attribute("Name").Value,
        Member = p.Attribute("Name").Value,
        Type = p.Attribute("Type").Value,
        Nullable = bool.Parse(p.Attribute("Nullable").Value),
    };

Answer 3

I stumbled upon this answer to solve my own problem and used Conrad Frix 's answer. The question specified VB.NET though and that is what I program in. Here are Conrad's answers in VB.NET (they may not be a perfect translation, but they work):

Example 1

    Dim PropertyNames1 = From Prprt In Type.GetType("LocalDB.tlbMeter").GetProperties()
                         Select Prprt.Name

Example 2

    Dim LocalDB2 As New LocalDBDataContext
    Dim bsmappping As New System.Data.Linq.Mapping.AttributeMappingSource()
    Dim bsmodel = bsmappping.GetModel(LocalDB2.GetType())
    Dim bstable = bsmodel.GetTable(LocalDB.tblMeters.GetType())

    Dim PropertyNames2 As IQueryable(Of String) = From fields In bstable.RowType.DataMembers
                                                  Where fields.IsPersistent = True
                                                  Select fields.Member.Name  'IsPersistant to only get the Column Mapped properties

Example 3

    Dim LocalDB3 As New LocalDBDataContext
    Dim qMeters = From mtr In LocalDB3.tblMeters
                  Select mtr


    Dim FirstResult As tblMeter = qMeters.First()
    Dim PropertyNames3 As List(Of String) = From FN In FirstResult.GetType().GetProperties()
                                            Select FN.Name.ToList()

To display the results:

    For Each FieldName In PropertyNames1
        Console.WriteLine(FieldName)
    Next

    For Each FieldName In PropertyNames2
        Console.WriteLine(FieldName)
    Next

    For Each FieldName In PropertyNames3
        Console.WriteLine(FieldName)
    Next

Please also read Conrad's answer for notes on each method!