Retrieving Data from LINQ to SQL in JSON format?

Question

Retrieving Data from LINQ to SQL in JSON format?

asp.net-web-api c# entity-framework json linq

Question

I have a problem with Serialization of Data from database to JSON format. I'm using WebAPI 2 and Entity Framework 6. I've created with EF a Model. The database and the tables with content are even created. When I use the code below I'm getting an error when I type http://localhost:54149/api/qr_group .

Controller:

private EfContext db = new EfContext();

// GET api/<controller>
public IEnumerable<QR_Group> GetGroups()
{
    var result = from g in db.QR_Groups
                 select g;
    return result.ToList();
}

I don't know how to use Newtonsoft.Json to serialize the table with the content in JSON format.

I've tried the following code instead of the code above:

public IQueryable<QR_Group> GetGroups()
{
  var groupList = (from g in db.QR_Groups
                   select new
                   {
                     name = g.name,
                     code = g.code
                   }).AsQueryable();

  var json = JsonConvert.SerializeObject(groupList);

  return json; //error CS0029: Cannot implicitly convert type `string' to `System.Linq.IQueryable<RestApi.Models.QR_Group>'
}

I get the error CS0029.. How can I solve this to return the data in json? As reminder: The QR_Group entity has 3 columns (Id, name, code)

yuro

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Simon Wang · Accepted Answer · 5/23/2017 12:14:09 PM

Specifically to your second function, JsonConvert.SerializeObject would just serialize any object into a JSON format string, which means you should return a string instead of an IQueryable<>.

So for the controller there are quite a few ways to return it back, like: In MVC, how do I return a string result?

EDIT:

Following code would be one way that should working:

Controller:

private EfContext db = new EfContext();

// GET api/<controller>
public ActionResult GetGroups()
{
    var groupList = (from g in db.QR_Groups
    select new
    {
        name = g.name,
        code = g.code
    }).AsQueryable();

    return Content(JsonConvert.SerializeObject(groupList));
}

Retrieving Data from LINQ to SQL in JSON format?

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