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This article mainly introduces "how to use ADO.NET applications". In daily operation, I believe many people have doubts about how to use ADO.NET applications. The editor consulted all kinds of materials and sorted out simple and easy-to-use operation methods. I hope it will be helpful to answer the doubts about "how to use ADO.NET applications". Next, please follow the editor to study!

CustomerID associates the Customers table with the Orders table. For each customer in the Customers table, all child rows in the Orders table are determined to return the number of orders for a particular customer and their OrderID value.

The extended example will also return values from the OrderDetails table and the Products table. The Orders table uses OrderID to associate with the OrderDetails table to determine the products and quantities ordered in each customer order. Since the OrderDetails table contains only the ProductID,OrderDetails of the ordered products, ProductID is associated with the Products to return the ProductName. In this relationship, the Products table is the parent table and the OrderDetails table is the child table. Therefore, when iterating through the OrderDetails table, GetParentRow is called to retrieve the relevant ProductName value.

Note that when creating an ADO.NET DataRelation for the Customers table and the Orders table, no value is specified for the createConstraints flag (the default is true). It assumes that all rows in the Orders table have a CustomerID value that exists in the parent Customers table. If CustomerID exists in an Orders table other than the Customers table, ForeignKeyConstraint throws an exception.

If the child column may contain values that the parent column does not contain, set the createConstraints flag to false when you add DataRelation. In this example, the DataRelation,createConstraints flag between the Orders table and the OrderDetails table is set to false. This allows the application to return all the records in the OrderDetails table and only a subset of the records in the Orders table without generating run-time exceptions. The extended example generates output in the following format.

To read data from a data source, an ADO.NET application must first create a connection object. The connection object can be SQLConnection or ADOConnection, depending on the target provider used. It is important to remember that although not recommended here, you can also use ADO .NET classes to connect to SQL Server databases. The disadvantage of this method is that the code needs to go through an unnecessary extra layer of code. First it calls into ADO's managed provider, then ADO's managed provider invokes the SQL Server OLE DB provider. As the OLE DB provider does, the SQL Server managed provider manipulates the data directly.

There is a DataAdapter class in each of these data providers, such as OleDbDataAdapter class in OLE DB .NET Framework data provider, SqlDataAdapter class in The SQL Server .NET Framework data provider, and OdbcDataAdapter class in The ODBC .NET Framework data provider. With these DataAdapter, you can retrieve data from the database and populate the tables in the DataSet.

At this point, the study on "how to use ADO.NET applications" is over. I hope to be able to solve your doubts. The collocation of theory and practice can better help you learn, go and try it! If you want to continue to learn more related knowledge, please continue to follow the website, the editor will continue to work hard to bring you more practical articles!

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