Build command objects and query data from data sources

DbCommand

You use the DbCommand object to send a SQL command to the data store.

DbCommand can be a Data Manipulation Language (DML) command to retrieve, insert, update, or delete data, as well as Data Definition Language (DDL) command, which enables you to create tables and modify schema information at the database.

Requirements

The DbCommand object requires:

• valid open connection

• valid value for its CommandText property

• valid value for its CommandType property

How to create

• pass a DbConnection object into the DbCommand object’s constructor

• attach a DbConnection object to the existing DbCommand object’s Connection property

• (the best way) use the CreateCommand method on the DbConnection object

Example

var nw = ConfigurationManager.ConnectionStrings["nw"];
var connection = new SqlConnection(nw.ConnectionString);
var cmd = connection.CreateCommand();
cmd.CommandType = CommandType.StoredProcedure;
cmd.CommandText = "CustOrderHist";
//don't forget to close the connection!

Methods

• ExecuteNonQuery. Use it when you don’t expect a command to return any rows—an insert, update, or delete query, for example.

• ExecuteReader. It returns a DbDataReader instance, which is a forward-only, read-only, server-side cursor.

• ExecuteScalar. Queries are often expected to return a single row with a single column. In these situations, the results can be treated as a single return value.