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Published: November 20, 2022 (1 week ago)

C DAL Generator For SQL Server And MS Access

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C DAL Generator For SQL Server And MS Access

another consideration is the need to manage versioning of stored procedures. if you are using stored procedures in your system, it is very important that you create a versioning scheme. versioning is necessary if you want to be able to roll back to a previous version of a stored procedure. if you have a bug in a stored procedure, you could easily roll back to a previous version that has the bug corrected. this is sometimes referred to as breaking changes, and versioning is very important for this reason. this is especially true when using a stored procedure as a replacement for ad hoc sql. as we know, the data developer writes sql queries to access data in the database, but the data architect designs the database. for these reasons, a versioning scheme for stored procedures is very important in a relational database environment. if you plan on using stored procedures, you need to make sure you understand the pitfalls of poor design, including not having a versioning scheme in place, and you need to ensure that you will be able to easily roll back to a previous version of a stored procedure if the need arises.

when developing the application data layer, keep in mind that it should not be considered a data access layer. the purpose of the data access layer is to connect the application layer and the data layer. in many cases, this is actually a database-specific implementation, and it is very important to keep the two layers separate when developing your application. if the data access layer is tightly coupled with the database or the rdbms in question, it will be difficult to make changes to the database. if this is the case, you might consider using sql server, mysql, or another rdbms. this is not to say that you should never use stored procedures, just that you should ensure that a clean separation is maintained between the layers of the application. you do not want to tie the data access layer to the database in such a way that if your application is re-written in another language, such as c++, the data access layer would need to be modified to accommodate the new language.

The data access layer is often implemented as a separate project for a few reasons. The obvious advantage is that you can reuse the data access layer in future development. For example, when you are working on a new application project, you can reuse your class library and any queries you have developed. When all of your client-side presentation layer code changes, your data access layer is less likely to break because you can change the data access code without reworking your client-side presentation layer code. This makes the data access layer relatively easy to maintain. Also, in my experience, there is rarely a good reason for your data access code to be in the same project as your presentation layer code. Having the data access layer code in a separate project is also useful when you want to perform SQL in a batch process, as we’ll see in the next tutorial. Finally, you can run the class library directly without the presentation layer or from within the presentation layer, if you so desire. The code below shows how we can implement the command syntax provider and create a connection for a new connection using DALConnectionManager:
dataservice.servicereference1.dataservicecontext context = new dataservice.dataservicecontext(); a dataservicecontext can be used to support any odata-based applications. to connect to a sql server database, we must generate a connection string and pass it to the constructor of the dataservicecontext. this is done with the following code:
the easiest way to understand what methods are in the dal for either database is to take a look at the class diagram, as discussed earlier. the northwind example class diagram can be seen below, in figure 1, in figure 1. as is shown, the northwind dal contains a single data access layer, denoted as dal. notice that this layer contains a single custom object data source called northwindcontext. in this example the context represents all the connections, statements, and so forth that are made to the underlying data source for use by the dal. classes such as northwindcontext, datatable, and datacolumn share certain methods such as addnew(); addnew(); addnew(); and so forth. these are the methods that are added to the classes when they are created from a database (i.e., from the server explorer). it is important to remember that the bll classes (which we will look at in the next section ) are not part of the data access layer. they only have to call methods that are added to the data access layer.