ADO.NET in a Nutshell

2017-07-07 02:10:07

A DataRow object represents a row of data in the table stored in a collection of columns . Rows belonging to the DataTable are stored as DataRow objects in a DataRowCollection object and are accessed through the Rows property of the DataTable . The Rows property accesses methods and properties that can add, remove, and examine the DataRow objects in a DataTable . This section examines some of the methods and properties of the DataRowCollection .

There are two methods that can add a row to a table. The Add( ) method takes either a DataRow argument or an object array of columns of the row to be added:

DataTable dt = new DataTable("MyTable"); dt.Columns.Add("Column1", typeof(System.Int32)); dt.Columns.Add("Column2", typeof(System.String)); DataRow newrow = dt.NewRow(); newrow["Column1"].Value = 1; newrow["Column2"].Value = "DataRow 1"; // add a row using a reference to a DataRow dt.Rows.Add(dr); // add and create a DataRow in one statement dt.Rows.Add(new Object[] {2, "DataRow 2"});

Additionally, a DataRow can be inserted at a specific point in the DataRowCollection using the InsertAt( ) method, which in addition to a reference to a DataRow , takes an argument specifying the zero-based index at which to insert the row.

// create a new row DataRow row = dt.NewRow(); row.ItemArray = new Object[] {1, "DataRow 1"}; // insert a new row as the first item of the collection dt.Rows.InsertAt(row, 0);

There are two methods that can examine and locate rows within the DataRow collection. The Contains( ) method returns a value indicating whether the primary key exists in the collection of rows. The method has two overloads that take an object or an array of objects and allow primary keys based on one or more columns to be examined.

// look for a primary key that is based on a single column Boolean exists = dt.Rows.Contains("PK Value 1"); // look for a primary key that is based on multiple columns Boolean exists = dt.Rows.Contains(new Object[] {"PK Field1 Value", "PK Field2 Value"});

The Find( ) method is the second method that can locate a row based on the primary key. The Find( ) method differs from the Contains( ) method in that it returns the matching row rather than just indicating if a matching row was found. Like the Contains( ) method, the Find( ) method has two overloads that take an object or an array of objects and allow primary keys based on one or more columns to be examined. A null reference is returned if a matching row isn't found:

// get the row for a primary key that is based on a single column DataRow row = dt.Rows.Find("PK Value 1"); // get the row for a primary key that is based on multiple columns DataRow row = dt.Rows.Find(new Object[] {"PK Field1 Value", "PK Field2 Value"});

The Remove( ) , RemoveAt( ) , and Clear( ) methods remove rows from the DataTable . The Remove( ) method takes a DataRow argument and removes that row from the collection:

// remove the row matching the primary key value, if found DataRow row = dt.Rows.Find("PK Value 1"); if(row! = null) dt.Rows.Remove(row);

The RemoveAt( ) method takes an argument that specifies the index within the collection at which to remove the row:

// remove the first row from the collection dt.Rows.RemoveAt(0);

Finally, the Clear( ) method removes all rows from the table:

// remove all rows from the table dt.Rows.Clear();

Rows are discussed in detail in Chapter 9.

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