.NET/Java PDF, Tiff, Barcode SDK Library

Represents Connection to a database Command to be executed by a database Parameter for a command Single row of data returned by a query; alternatively, the IDataRecord interface represents the same concept Iterator over the full results returned by a query (potentially many rows and many row sets); implements

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* The name is a little confusing. In a sense, ADO.NET is a successor to ADO (ActiveX Data Objects), a data access system that was around before .NET. So ADO.NET does for . NET what ADO did for Visual Basic 6. But they are quite different technologies ADO.NET makes no use of ADO, or ActiveX. ADO.NET can use OLE DB, the technology underpinning ADO, but native ADO.NET providers are preferred the OLE DB provider is mainly for legacy sources.

Example 14-1 shows the typical pattern of communication. It starts by creating a connection object a SqlConnection here because this code connects to SQL Server, but for other databases you d use other types derived from DbConnection, such as Oracle Connection. Next, it builds a command object, setting its CommandText to the SQL we want the database to execute. This particular example is a parameterized command it selects addresses from a specified state, so we supply the command with a parameter object specifying the state. Then we execute the command by calling ExecuteReader, using the data reader object it returns to iterate through the rows produced by the query, and we print out the values. (This particular example assumes you have a SQL Server instance called .\SQLEXPRESS. If you installed the full edition or developer edition of SQL Server, specify just . instead of .\SQLEXPRESS. See Getting up and running with SQL Server 2008 Express on page 547 for information on getting the samples installed.)

string sqlConnectionString = @"Data Source=.\sqlexpress;" + "Initial Catalog=AdventureWorksLT2008;Integrated Security=True"; string state = "California"; using (DbConnection conn = new SqlConnection(sqlConnectionString)) using (DbCommand cmd = conn.CreateCommand()) { cmd.CommandText = "SELECT AddressLine1, AddressLine2, City FROM SalesLT.Address WHERE " + "StateProvince=@state"; DbParameter stateParam = cmd.CreateParameter(); stateParam.ParameterName = "@state"; stateParam.Value = state; cmd.Parameters.Add(stateParam); conn.Open(); using (DbDataReader reader = cmd.ExecuteReader()) { while (reader.Read()) { string addressLine1 = reader.GetString(0); // AddressLine2 is nullable, so we need to be prepared to get // back either a string or a DBNull string addressLine2 = reader.GetValue(1) as string; string city = reader.GetString(2); Console.WriteLine(addressLine1); Console.WriteLine(addressLine2); Console.WriteLine(city);

2, Qt 422 PASS : DateTest::initTestCase() FAIL! : DateTest::testAdd(Twenty days) Compared values are not the same Actual (nextyear()): 1979 Expected ("year"): 2979 datetestcpp(18) : failure location PASS : DateTest::testValid() PASS : DateTest::cleanupTestCase() Totals: 3 passed, 1 failed, 0 skipped ********* Finished testing of DateTest ********* The consequences of shifting to data-driven tests are summarized in the following list: Less code: You implement the test only once, but run different cases using that one test Less code redundancy: Because the test is only implemented once, it is not duplicated This also means not having to fix bugs in all tests if something is wrong Potentially better failure messages: Because each test vector row has a name, you can clearly see which case failed Some test cases can no longer be performed: This is a drawback.

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3. Finally, drag and drop an Input (Button) control onto the page. Your screen should look like Figure 4-1.

Because the test vector always contains data, it is hard to use it for testing some special cases (for instance, an empty constructor) This would require you to have a special case in your test code and a flag indicating no data, which would clutter the test code The last point can be fixed by putting these tests in a non data-driven test case It is not a limitation because they can be combined with data-driven tests in one class..

You might be wondering why we re fiddling around with parameter objects when it would have been simpler to just put the state directly into the SQL string This particular example hardcodes the state, so that would have worked, but the technique here would be important if the value was picked at runtime In general, building SQL queries with string concatenation is a dangerous thing to do if any of the text comes from outside your code (eg, from a form on a web page, or part of a URL) your code will be vulnerable to a SQL injection attack Imagine that Example 14-1 was part of a web application, and state here came from part of a URL such as http://examplecom/showinfo state=California.