C# – Selecting a single item with linq2sql query

clinqlinq-to-sql

I'm trying to retrieve a single entity from a Linq2Sql query, but I'm having trouble finding the 'pretty' way of doing it. Here's what I've found that works:

 var states = from state in dc.States where state.Id == j.StateId select state;
State s = states.ToList<State>().ToList()[0];

I'm hoping this isn't the best way of getting the entity. 😛

Anyone have a better solution?

Thanks in advance!

–J

Best Answer

try this:

int stateID = getTheStateIDToLookup();    
State state = dc.States.SingleOrDefault(s => s.StateID == stateID);

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C# – LINQ query on a DataTable

You can't query against the DataTable's Rows collection, since DataRowCollection doesn't implement IEnumerable<T>. You need to use the AsEnumerable() extension for DataTable. Like so:

var results = from myRow in myDataTable.AsEnumerable()
where myRow.Field<int>("RowNo") == 1
select myRow;

And as @Keith says, you'll need to add a reference to System.Data.DataSetExtensions

AsEnumerable() returns IEnumerable<DataRow>. If you need to convert IEnumerable<DataRow> to a DataTable, use the CopyToDataTable() extension.

Below is query with Lambda Expression,

var result = myDataTable
    .AsEnumerable()
    .Where(myRow => myRow.Field<int>("RowNo") == 1);

C# – Max or Default

Since DefaultIfEmpty isn't implemented in LINQ to SQL, I did a search on the error it returned and found a fascinating article that deals with null sets in aggregate functions. To summarize what I found, you can get around this limitation by casting to a nullable within your select. My VB is a little rusty, but I think it'd go something like this:

Dim x = (From y In context.MyTable _
         Where y.MyField = value _
         Select CType(y.MyCounter, Integer?)).Max

Or in C#:

var x = (from y in context.MyTable
         where y.MyField == value
         select (int?)y.MyCounter).Max();

Best Answer

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C# – LINQ query on a DataTable

C# – Max or Default

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