LINQ to map a datatable into a list

问题:

I just discover LINQ so be comprehensive with me please! :-)

So! I have a Data-tier who provide me datatables and i want to convert them into lists of objects. These objects are defined in a spécific layer DTO (Data transfer Objects).

How can I map every rows of my datatable into objects and put the all objects into a list? (today i make it "manually" field after field) Is it possible with LINQ? I've heard about LINQ2Entities? am i right?

Thanks to help a beginner to understand...

回答1:

If the objects is not too complex you can use this:

public static class DataTableExtensions
{
   public static IList<T> ToList<T>(this DataTable table) where T : new()
   {
      IList<PropertyInfo> properties = typeof(T).GetProperties().ToList();
      IList<T> result = new List<T>();

      foreach (var row in table.Rows)
      {
         var item = CreateItemFromRow<T>((DataRow)row, properties);
         result.Add(item);
      }

      return result;
   }

   private static T CreateItemFromRow<T>(DataRow row, IList<PropertyInfo> properties) where T : new()
   {
       T item = new T();
       foreach (var property in properties)
       {
           property.SetValue(item, row[property.Name], null);
       }
       return item;
   }
}

With that in place you can now write: var list = YourDataTable.ToList<YourEntityType>().

You can read about it here: http://blog.tomasjansson.com/convert-datatable-to-generic-list-extension/

And it is an answer to a previous question: Convert DataTable to Generic List in C#

EDIT: I should add that this is not linq, but some extension methods to DataTable I wrote. Also, it is working with the convention that the properties in the object you're mapping with has the same name as in the DataTable. Of course this could be extended to read attributes on the properties or the method itself could take a simple Dictionary<string,string> that could be used to do the mapping. You could also extend it with some functionality that take a params string[] excludeProperties that could be used to exclude some of the properties.

回答2:

I would suggest reading about The ADO.NET Entity Framework. It supports what you're asking, and the link should provide you with sufficient information and examples :)

There are also plenty of tutorials out there about the topic to get you started.

回答3:

it's better to Check if the column exist in the row to do the mapping another way it will throw an exception, in my case I have two objects one of them have more proprieties than the other with the same name and data type

  private static T CreateItemFromRow<T>(DataRow row, IList<PropertyInfo> properties) where T : new()
   {
       T item = new T();
       foreach (var property in properties)
       {  
           if (row.Table.Columns.Contains(property.Name))
           {
           property.SetValue(item, row[property.Name], null);
           }
       }
       return item;
   }