向数据表数据类型nvarchar添加列

Question

I declared a new dataset. Then added a datatable to it using the following command

DataTable newtable = ds.Tables.Add("returnresult");

now am trying to include two columns in this datatable with datatype "nvarchar". But the usual command for this does not accept nvarchar as a datatype

 newtable.Columns.Add("UniqueID",typeof());

using this command does not show nvarchar in the datatypes. is there any other command to get nvarchar as the datatype for columns?

Answer 1

The type nvarchar is a database type, the DataTable is an in-memory objectThe type nvarchar / varchar is string which is the default type if you add a column.

So this creates and adds a DataColumn of type string to the table:

newtable.Columns.Add("UniqueID");  // or:
newtable.Columns.Add("UniqueID", typeof(string));

If you want to specify the maximum length of a text column use it's MaxLength property.

But if you fill a DataTable from database you should use DataAdapter.Fill which automaticially infers the type and length from the database type.

The DataType property supports the following base .NET Framework data types:

Boolean
Byte
Char
DateTime
Decimal
Double
Guid
Int16
Int32
Int64
SByte
Single
String
TimeSpan
UInt16
UInt32
UInt64
Byte[]

Answer 2

In .NET, string is the equivalent of NVARCHAR(Any Length) , VARCHAR(Any Length) , etc...

Try: newtable.Columns.Add("UniqueID",typeof(string));

Answer 3

        DataTable newtable = ds.Tables.Add("returnresult");
        DataColumn newcolumn = newtable.Columns.Add("UniqueID", typeof(string));
        //newcolumn.MaxLength = n;   // nchar(n)
        newcolumn.MaxLength = 536.870.912; //nvarchar(max)  Variable-length Unicode data. Max 536.870.912 chars.