C# – String.IsNullOrEmpty in LINQ To SQL query

clinq-to-sql

My DBML exposes a record set that has a nullable nvarchar field. This nullable nvarchar field is represented as a string in my C# code.

Sometimes this field is null, sometimes it is an empty string, and sometimes it actually has a value.

Does String.IsNullOrEmpty() work in LINQ To SQL? For instance, would the following work:

var results = from result in context.Records
              where String.IsNullOrEmpty(result.Info) == false
              select result;

Best Answer

Curiously, per MSDN String.IsNullOrEmpty is supported (by virtue of it not being unsupported), yet I can only find complaints about it not being supported.

However, if it does work you should not explicitly compare it to a boolean value, instead:

var results = from result in context.Records
          /*XXX broke :( where !String.IsNullOrEmpty(result.Info) */
          where !(result.Info == null || result.Info.Equals(""))
          select result;

Related Solutions

.net – Entity Framework vs LINQ to SQL

LINQ to SQL only supports 1 to 1 mapping of database tables, views, sprocs and functions available in Microsoft SQL Server. It's a great API to use for quick data access construction to relatively well designed SQL Server databases. LINQ2SQL was first released with C# 3.0 and .Net Framework 3.5.

LINQ to Entities (ADO.Net Entity Framework) is an ORM (Object Relational Mapper) API which allows for a broad definition of object domain models and their relationships to many different ADO.Net data providers. As such, you can mix and match a number of different database vendors, application servers or protocols to design an aggregated mash-up of objects which are constructed from a variety of tables, sources, services, etc. ADO.Net Framework was released with the .Net Framework 3.5 SP1.

This is a good introductory article on MSDN: Introducing LINQ to Relational Data

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);

Best Answer

Related Solutions

.net – Entity Framework vs LINQ to SQL

C# – LINQ query on a DataTable

Related Topic