Could not find an implementation of the query pattern

Question

In my silverlight application I am trying to create a database connection using LINQ. First I add a new LINQ to SQL class, and drag my table called "tblPersoon" into it.

Then in my service file I try to execute the following query:

[OperationContract]
public tblPersoon GetPersoonByID(string id)
{
    var query = (from p in tblPersoon where p.id == id select p).Single();

But at tblPersoon it gives me the following error.

Could not find an implementation of the query pattern for source type 'SilverlightApplication1.Web.tblPersoon'. 'Where' not found.

And even when I try the following:

var query = (from p in tblPersoon select p).Single();

It gives me an error saying 'Select' not found!

Code for the generated class for my table can be found here: http://pastebin.com/edx3XRhi

What is causing this and how would I possibly solve this?

Thank you.

Answer 1

Is the tblPersoon implementing IEnumerable<T>? You may need to do it using:

var query = (from p in tblPersoon.Cast<Person>() select p).Single();

This kind of error (Could not find an implementation of the query pattern) usually occurs when:

• You are missing LINQ namespace usage (using System.Linq)
• Type you are querying does not implement IEnumerable<T>

Edit:

Apart from fact you query type (tblPersoon) instead of property tblPersoons, you also need an context instance (class that defines tblPersoons property), like this:

public tblPersoon GetPersoonByID(string id)
{
    var context = new DataClasses1DataContext();
    var query = context.tblPersoons.Where(p => p.id == id).Single();
    // ...

Answer 2

You may need to add a using statement to the file. The default Silverlight class template doesn't include it:

using System.Linq;

Answer 3

Make sure these references are included:

• System.Data.Linq
• System.Data.Entity

Then add the using statement

using System.Linq;

Answer 4

You must have forgotten to add a using statement to the file like this:

using System.Linq;

Answer 5

I had a similar issue with generated strongly typed datasets, the full error message was:

Could not find an implementation of the query pattern for source type 'MyApp.InvcHeadDataTable'. 'Where' not found. Consider explicitly specifying the type of the range variable 'row'.

From my code:

        var x =
            from row in ds.InvcHead
            where row.Company == Session.CompanyID
            select row;

So I did as it suggested and explicitly specified the type:

        var x =
            from MyApp.InvcHeadRow row in ds.InvcHead
            where row.Company == Session.CompanyID
            select row;

Which worked a treat.

Answer 6

You are missing an equality:

var query = (from p in tblPersoon where p.id == 5 select p).Single();

where clause must result in a boolean.

OR you should not be using where at all:

var query = (from p in tblPersoon select p).Single();

Answer 7

For those of you (like me) that wasted too much time from this error:

I had received the same error: "Could not find implementation of query Pattern for source type 'DbSet'" but the solution for me was fixing a mistake at the DbContext level.

When I created my context I had this:

public class ContactContext : DbContext
    {
        public ContactContext() : base() { }

        public DbSet Contacts { get; set; }
    }

And my Repository (I was following a Repository pattern in ASP.NET guide) looked like this:

public Contact FindById(int id)
    {       
        var contact = from c in _db.Contacts where c.Id == id select c;
        return contact;
    }

My issue came from the initial setup of my DbContext, when I used DbSet as a generic instead of the type.

I changed public DbSet Contacts { get; set; } to public DbSet<Contact> Contacts { get; set; } and suddenly the query was recognized.

---

This is probably what k.m says in his answer, but since he mentioned IEnumerable<t> and not DbSet<<YourDomainObject>> I had to dig around in the code for a couple hours to find the line that caused this headache.

Answer 8

I had the same error as described by title, but for me it was simply installing Microsoft access 12.0 oledb redistributable to use with LinqToExcel.

Answer 9

Hi easiest way to do this is to convert this IEnumerable into a Queryable

If it is a queryable, then performing queries becomes easy.

Please check this code:

var result = (from s in _ctx.ScannedDatas.AsQueryable()
                              where s.Data == scanData
                              select s.Id).FirstOrDefault();
                return "Match Found";

Make sure you include System.Linq. This way your error will be resolved.

Answer 10

I had the same error, but for me, it was attributed to having a database and a table that were named the same. When I added the ADO .NET Entity Object to my project, it misgenerated what I wanted in my database context file:

// Table
public virtual DbSet<OBJ> OBJs { get; set; }

which should've been:

public virtual DbSet<OBJ> OBJ { get; set; }

And

// Database?
public object OBJ { get; internal set; }

which I actually didn't really need, so I commented it out.

I was trying to pull in my table like this, in my controller, when I got my error:

protected Model1 db = new Model1();

public ActionResult Index()
{
    var obj =
        from p in db.OBJ
        orderby p.OBJ_ID descending
        select p;

    return View(obj);
}

I corrected my database context and all was fine, after that.