Bind webgrid to EF query result - Error_7_Argument 1: cannot convert from 'ProviderRxTransaction' to 'System.Collections.Generic.IEnumerable<dynamic>'

Question

User379720387 posted

This is the equivalent of a db.QuerySingle:

var rx1 = dbContext.ProviderRxTransactions
        .Include("ProviderService.Service")
        .Where(t => t.transactionId == transactionid).FirstOrDefault();

var grid = new WebGrid(rx1, rowsPerPage: 20);

How can I bind the webgrid to rx1?

Answer 1

User-821857111 posted

The WebGrid is designed to display collections as rows of data. Your query only returns a single object. If you really want to use the grid to display details of one object change the query to return a collection:

var rx1 = dbContext.ProviderRxTransactions
        .Include("ProviderService.Service")
        .Where(t => t.transactionId == transactionid).ToList();

Obviously if more than one item has the same transactionId, they will be displayed too. 

Answer 2

User-691209617 posted

The simplest fix is just to use the Cast<> LINQ operator:

public IEnumerable<IMyType> All() {
var query = _connection.Query("SELECT * FROM [table]");
return query.Select(o => _myTypeFactory.Create(o))
.Cast<IMyType>();
}

Alternatively, you could cast each element:
public IEnumerable<IMyType> All() {
var query = _connection.Query("SELECT * FROM [table]");
return query.Select(o => (IMyType) _myTypeFactory.Create(o));
}

It doesn't currently work because there's simply no implicit conversion available between IEnumerable<dynamic> and IEnumerable<IMyType>. IEnumerable<dynamic> could be implemented in any number of ways, and given that each item will be generated dynamically there's no reason to suppose the result value will implement IEnumerable<IMyType>.

I agree that it looks like the second form isn't actually adding anything, but the compiler doesn't check all the possible return types of _myTypeFactory.Create(o) - it treats that whole expression as a dynamic value, i.e. the expression is of type dynamic. Therefore the Select result is still of type IEnumerable<dynamic>.

Another option is to specify the generic type argument to Select.

public IEnumerable<IMyType> All() {
var query = _connection.Query("SELECT * FROM [table]");
return query.Select<IMyType>(o => _myTypeFactory.Create(o));
}
That's attempting to force the lambda expression to a Func<dynamic, IMyType> - I believe that will work...

Answer 3

User-821857111 posted

The simplest fix is just to use the Cast<> LINQ operator:

Huh??? What question are you answering?