Strongly Typed Access to Data in a Typed Data Set in VS .NET

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Listing 22 Strongly Typed Access to Data in a Typed Data Set
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public void UpdateCustomer(CustomersDataSet custData, string custID, string compName, string contactName, string title, string phone) { string custIDColumnName = custDataCustomersCustomerIDColumnColumnName; CustomersDataSetCustomersRow[] rows = (CustomersDataSetCustomersRow[])dsCustomersSelect( custIDColumnName + "='" + custID + "'"); CustomersDataSetCustomerRow row = rows[0]; rowCompanyName = compName; rowContactName = contactName; rowContactTitle = title; rowPhone = phone; }
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Although this code may look slightly more verbose due to the nested type definitions for the CustomersRow under the CustomersDataSet, the beauty of the code in Listing 22 is that there aren't any hard-coded schema references There aren't any string literals for table or column names, and you don't have to index any column positions because you can more easily and clearly get to them through the typed properties exposed on the typed row object The CustomerIDColumn public property on the table class and the ColumnName property on the DataColumn instance it represents gets to the column name without having to be hard coded By doing this, even if the schema changes, the code won't necessarily have to
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The other part that isn't apparent from a block of code like this is actually one of the best benefits of typed data sets from a productivity standpoint: IntelliSense! Because of the type definitions that underlie this code, you get full IntelliSense on the properties and methods that the typed classes add So if you haven't memorized all the column names exactly, you can just scroll through the member names after typing the "" next to the typed data row variable to locate a column So what happens if the database schema changes and the DBA decides to rename the Phone column to PhoneNo Well, as long as the DBA at least tells you of the change, you can quickly regenerate the CustomersDataSet class and its contained classes, and recompile If you do this, anywhere in your code that you referenced the CustomersRowPhone property, you would get a compiler error like the following: D:\Code\ 2\TypedDataSets\Form1cs(25,17): error CS0117: 'TypedDataSetsCustomersDataSetCustomersRow' does not contain a definition for 'Phone'
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You could simply click through the compiler errors in the Task pane in Visual Studio, change the column names to PhoneNo instead of Phone, and try to compile again You could also resolve this by changing the Name property of the PhoneNo column back to Phone after regenerating the data set, and leave the Source property set to PhoneNo If the DBA had changed the type of the column instead of the name, you would get the following errors for each of those references: D:\Code\ 2\TypedDataSets\Form1cs(25,25): error CS0029: Cannot implicitly convert type 'string' to 'int'
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This is a huge benefit Granted that you would still have to click through all the compiler errors and decide how to resolve them Of course, maybe you would decide to do a global find-and-replace operation or use some of the refactoring tools that are new in Visual Studio 2005 But the big difference between using the typed data set classes and when you were coding against the tables and columns using strings for their names is that you are pretty much guaranteed by the compiler that you will find all the affected lines of codeas long as you only program against the type-safe properties of the typed data set, table, and row It may be tempting at times to use some of the properties and methods of the DataSet base class, such as theRows or Columns collection These are still exposed on your typed data set class because they derive from DataSet However, you should try to get any untyped reference back into a typed variable reference as quickly as possible so that you can maintain the benefit of using typed data sets throughout your code When you do need to use one of the base class methods that returns an untyped row, such as the Select method shown in Listing 22, make sure to cast the result to the typed version of the row before you use it so that you can take full advantage of the type safety provided by the typed data sets To fill a typed data set or update a data source using a typed data set, you use code almost exactly like what you saw at the beginning of the chapter for filling an untyped data set Because the typed data set is a derived class from DataSet, the data adapter uses methods of the base DataSet class to populate the typed data set instance during aFill operation and to extract and propagate changes during an Update operation This was how you had to work with typed data sets in NET 1X, and the problem was that you had to throw away some type safety at the point you interacted with the data source How do you know whether the data adapter is configured properly to work with that strongly typed data set You don't, and so you won't find out about errors again until runtime In NET 20, a new construct brings type safety to the adapter between a data source and a type-safe data set That construct, called a table adapter, will be discussed in detail later in this chapter
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