How to select a single column with Entity Framework?

Question

Is there a way to get the entire contents of a single column using Entity Framework 4? The same like this SQL Query:

SELECT Name FROM MyTable WHERE UserId = 1;

Answer 1

You can use LINQ's .Select() to do that. In your case it would go something like:

string Name = yourDbContext
  .MyTable
  .Where(u => u.UserId == 1)
  .Select(u => u.Name)
  .SingleOrDefault(); // This is what actually executes the request and return a response

If you are expecting more than one entry in response, you can use .ToList() instead, to execute the request. Something like this, to get the Name of everyone with age 30:

string[] Names = yourDbContext
  .MyTable
  .Where(u => u.Age == 30)
  .Select(u => u.Name)
  .ToList();

Answer 2

I'm a complete noob on Entity but this is how I would do it in theory...

var name = yourDbContext.MyTable.Find(1).Name;

If It's A Primary Key.

-- OR --

var name = yourDbContext.MyTable.SingleOrDefault(mytable => mytable.UserId == 1).Name;

-- OR --

For whole Column:

var names = yourDbContext.MyTable
.Where(mytable => mytable.UserId == 1)
.Select(column => column.Name); //You can '.ToList();' this....

But "oh Geez Rick, What do I know..."

Answer 3

Using LINQ your query should look something like this:

public User GetUser(int userID){

return
(
 from p in "MyTable" //(Your Entity Model)
 where p.UserID == userID
 select p.Name
).SingleOrDefault();

}

Of course to do this you need to have an ADO.Net Entity Model in your solution.

Answer 4

您可以使用 LINQ select子句并引用与您的 Name 列相关的属性。

Answer 5

If you're fetching a single item only then, you need use select before your FirstOrDefault()/SingleOrDefault() . And you can use anonymous object of the required properties.

var name = dbContext.MyTable.Select(x => new { x.UserId, x.Name }).FirstOrDefault(x => x.UserId == 1)?.Name;

Above query will be converted to this:

Select Top (1) UserId, Name from MyTable where UserId = 1;

For multiple items you can simply chain Select after Where:

var names = dbContext.MyTable.Where(x => x.UserId > 10).Select(x => x.Name);

Use anonymous object inside Select if you need more than one properties.