The ObjectDataSource s parameters mapped to the input parameters for the methods in the Business Logic Layer. These similarities also extend to parameters. In the previous tutorial we compared the ObjectDataSource which has been our tool of choice over the first 46 tutorials with the SqlDataSource, noting their conceptual similarities.
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In this tutorial, we'll see how to define parameterized queries as well as how to specify the parameter values both declaratively and programmatically. Moreover, the parameter values can be automatically pulled from a variety of sources the querystring, session state, controls on the page, and so on or can be assigned programmatically. WHERE UnitPrice > SqlDataSource supports parameterized queries, both for SELECT statements and INSERT, UPDATE, and DELETE statements. With Microsoft SQL Server, parameters are denoted using as in: SELECT ProductName
Ideally, such inputs are specified through the use of parameters. Typically, the values used in a WHERE clause are determine by some external source, such as a querystring value, a session variable, or user input from a Web control on the page. For example, to display the names of products costing more than $50.00, we could use the following query: SELECT ProductName In a SELECT statement, the WHERE clause can be used to limit the results returned. The SQL SELECT statements used in the previous tutorial s demos lacked WHERE clauses. Whether selecting columns from a table or view or entering a custom SQL statement, the SqlDataSource control s SelectCommand property is assigned the resulting ad-hoc SQL SELECT statement and it is this SELECT statement that is executed when the SqlDataSource s Select() method is invoked (either programmatically or automatically from a data Web control). Using the Configure Data Source wizard, we could choose the database and then either: pick the columns to return from a table or view enter a custom SQL statement or use a stored procedure. In the previous tutorial we saw how to use the SqlDataSource control to retrieve data directly from a database. The parameters can be specified both declaratively and programmatically, and can be pulled from a number of locations such as the querystring, Session state, other controls, and more. In this tutorial, we continue our look at the SqlDataSource control and learn how to define parameterized queries.
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