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Synchronize Your Databases with .NET Web Services (Part II)  : Page 5

When data gets created in many locations, you often need to create a process that collects and copies this data to multiple sites. In this article, you'll see how to use Web services to automatically synchronize remote databases in a decentralized way, by letting each machine query the others until they all contain the same data.


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The TestSQLStatement Method
This second public Web method is actually a debugging tool left in place to help when testing the service and client application. The method simply returns a string containing the SQL statement to use when calling the Web service to extract the data with the specified set of parameter values. Internally, it calls the GetSQLStatement function shown earlier with three parameters. Note that this method accepts only a single table name:

<WebMethod(Description:= _ "Returns the SQL statement for testing" _ )> Public Function TestSQLStatement( _ sHostIP As String, _ sTableName As String, _ dFromDate As Date) As String Return GetSQLStatement(sHostIP, sTableName, dFromDate) End Function

Of course, you could just expose the GetSQLStatement function as a Web method directly, instead of creating this "wrapper" call to it. However, after testing, you'll probably want to remove this public method, and you can do this just by deleting the wrapper Web method rather than having to edit the declarations of the GetSQLStatement function.

Figure 6 shows the result of calling the TestSQLStatement method. Because the table used for the query contains columns that hold year and week numbers rather than a single date field, the GetSQLStatement function generates a WHERE clause that specifies the appropriate year and week values:



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