convert int to string in linq for searching

问题:

I would like my users to be able to search for purchase orders (which are INT's) via partial strings, i.e. if a purchase order is 123456 typing in 456 gives me 123456 in the results.

I thought this would work:

        var pop = (from po in ctx.PurchaseOrders
               let poid = po.PurchaseOrderID.ToString()
               where poid.Contains(term)
               select new SearchItem
               {
                   id = poid,
                   label = po.SupplierID,
                   category = "purchaseorder"
               }).ToList();

But I get an error

LINQ to Entities does not recognize the method 'System.String ToString()' method, and this method cannot be translated into a store expression.

How can I convert the INT PurchaseOrderID to a string to enable me to search for fragments of it?

Thanks

回答1:

Use this:

id = SqlFunctions.StringConvert((double)poid)

For more: http://msdn.microsoft.com/en-us/library/dd487127.aspx

回答2:

For future reference, have fixed this by using:

    var pop = ctx
    .PurchaseOrders
    .OrderBy(x => x.PurchaseOrderID)
    .ToList()
    .Select(x => new SearchItem()
    {
        id = x.PurchaseOrderID.ToString(),
        label = x.SupplierID,
        category = "purchaseorder"
    });

It's the intermediary list that makes it work.

回答3:

You're getting that error because your LINQ to SQL doesn't recognize the ToString() method.

If you want to convert an int to a string and you're using SQL Server with EF, use the function SqlFunctions.StringConvert in this way:

let poid = SqlFunctions.StringConvert((double)po.PurchaseOrderID);

or this, as alternative:

where Convert.ToString(po.PurchaseOrderID).Contains(term)

The problem is that we don't know what is the provider you're using with EF. In the case of SQL Server, this will work, but if the provider is different, like MySQL, using that expression, the application will throw an exception with this message:

The specified method System.String StringConvert on the type 'System.Data.Objects.SqlClient.SqlFunctions' cannot be translated into a LINQ to Entities store expression.

Be careful!

In the case you're not using SQL Server as provider, use an explicit cast in your query, as suggested by @SimonBelanger:

let poid = (string)po.PurchaseOrderID

回答4:

I stumbled upon this question and wanted to post a solution that will work with Entity Framework and LINQ to entities via Lambda expression.

 db.PurchaseOrders.AsEnumerable()
 .Where(x => x.PurchaseOrderID.ToString().Contains(term))
 .ToList();

which was borrowed from the solution here --> https://stackoverflow.com/a/21234785/2395030

回答5:

Linq dont know what ToString() Method is, however you can define your custom method. If you use this link, you get your problem solved.

回答6:

try this

var pop = (from po in ctx.PurchaseOrders
               let poid = SqlFunctions.StringConvert((double)po.PurchaseOrderID)
               where poid.Contains(term)
               select new SearchItem
               {
                   id = poid,
                   label = po.SupplierID,
                   category = "purchaseorder"
               }).ToList();