CODEWITHSUNDEEP
c#namespacesvar
Visakh V A
Visakh V A

Reputation: 320

var key word and using name space

I have a method ExecuteQuery and it is returning a Datatable object which is a method of object _dataAccess, this will compile proper with out using System.Data

string query = "select * from UserNeeds where userNeedID =" + item.ParentId;
var result = _dataAccess.ExecuteQuery(query, CommandType.Select);
foreach (var rows in result.Rows)
{

}

but if i changed var and if give orginal type Datatable it will show comiple time error as we missed System.Data.

My question is how compiler can understand that System.Data is the name space when we keep var as type.

or why it is forcing when we use orginal datatype in place of var, how compiler handing the same ?

Upvotes: 0

Views: 68

Answers (2)

Ashutosh Kumar Singh
Ashutosh Kumar Singh

Reputation: 36

Namespace is a short notation of any object. If you dont specify then you need to give the full object name.

Var is a one time dynamic data type which stores the object types once it creates dynamically with full object name.

Upvotes: 0

Tim Schmelter
Tim Schmelter

Reputation: 460058

var is not a type by itself, it's a placeholder for the actual type which will be resolved by the compiler. Since DataRowCollection(returned by DataRable.Rows) does not implement IEnumerable<DataRow> but only the non-generic IEnumerable interface the foreach object rows is of type Object. So you can't use DataRow properties and methods in the loop.

You need to cast it everytime or let it be casted by the foreach:

foreach (DataRow row in result.Rows)
{

}

Now you need to add using System.Data to the top of your file or use 

foreach (System.Data.DataRow row in result.Rows)
{

}

So the reason why it compiles with var without adding the namespace is that the compiler uses System.Object for the var because DataRowCollection yields objects not DataRows.

Upvotes: 2

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