One of the neat features of SQL Server 2005 is the integration with the .NET CLR. The integration of CLR with SQL Server extends the capability of SQL Server in several important ways. This integration enables developers to create database objects such as stored procedures, user defined functions, and triggers by using modern object-oriented languages such as VB.NET and C#.
In this post, I will demonstrate how to create the stored procedures using C#. Before looking at the code, let us understand the pros and cons of using managed language in the database tier to create server side objects.
T-SQL Vs Managed Code
Although T-SQL, the existing data access and manipulation language, is well suited for set-oriented data access operations, it also has limitations. It was designed more than a decade ago and it is a procedural language rather than an object-oriented language. The integration of the .NET CLR with SQL Server enables the development of stored procedures, user-defined functions, triggers, aggregates, and user-defined types using any of the .NET languages.
This is enabled by the fact that the SQL Server engine hosts the CLR in-process. All managed code that executes in the server runs within the confines of the CLR. The managed code accesses the database using ADO.NET in conjunction with the new SQL Server Data Provider. Both Visual Basic .NET and C# are modern programming languages offering full support for arrays, structured exception handling, and collections.
Developers can leverage CLR integration to write code that has more complex logic and is more suited for computation tasks using languages such as Visual Basic .NET and C#. Managed code is better suited than Transact-SQL for number crunching and complicated execution logic, and features extensive support for many complex tasks, including string handling and regular expressions. T-SQL is a better candidate in situations where the code will mostly perform data access with little or no procedural logic.
Creating CLR Based Stored Procedures
For the purposes of this example, create a new SQL Server Project using Visual C# as the language of choice in Visual Studio 2005. Since you are creating a database project, you need to associate a data source with the project. At the time of creating the project, Visual Studio will automatically prompt you to either select an existing database reference or add a new database reference. Choose pubs as the database. Once the project is created, select Add Stored Procedure from the Project menu. In the Add New Item dialog box, enter Authors.cs and click Add button. After the class is created, modify the code in the class to look like the following.
using System;
using System.Data;
using System.Data.Sql;
using System.Data.SqlClient;
using System.Data.SqlTypes;
using Microsoft.SqlServer.Server;
public class Authors
{
[SqlProcedure]
public static void GetAuthors()
{
SqlPipe sp = SqlContext.Pipe;
using (SqlConnection conn = new
SqlConnection("context connection=true"))
{
conn.Open();
SqlCommand cmd = new SqlCommand();
cmd.CommandType = CommandType.Text;
cmd.Connection = conn;
cmd.CommandText = "Select DatePart(second, GetDate()) " +
" As timestamp,* from authors";
SqlDataReader rdr = cmd.ExecuteReader();
sp.Send(rdr);
}
}
[SqlProcedure]
public static void GetTitlesByAuthor(string authorID)
{
string sql = "select T.title, T.price, T.type, " +
"T.pubdate from authors A" +
" inner join titleauthor TA on A.au_id = TA.au_id " +
" inner join titles T on TA.title_id = T.title_id " +
" where A.au_id = '" + @authorID + "'";
using (SqlConnection conn = new
SqlConnection("context connection=true"))
{
conn.Open();
SqlPipe sp = SqlContext.Pipe;
SqlCommand cmd = new SqlCommand();
cmd.CommandType = CommandType.Text;
cmd.Connection = conn;
cmd.CommandText = sql;
SqlParameter paramauthorID = new
SqlParameter("@authorID", SqlDbType.VarChar, 11);
paramauthorID.Direction = ParameterDirection.Input;
paramauthorID.Value = authorID;
cmd.Parameters.Add(paramauthorID);
SqlDataReader rdr = cmd.ExecuteReader();
sp.Send(rdr);
}
}
}
Let us examine the above lines of code. The above code starts by importing the required namespaces and then declares a class named Authors. There are two important classes in the Microsoft.SqlServer.Server namespace that are specific to the in-proc provider:
- SqlContext: This class encapsulates the extensions required to execute in-process code in SQL Server 2005. In addition it provides the transaction and database connection which are part of the environment in which the routine executes.
- SqlPipe: This class enables routines to send tabular results and messages to the client. This class is conceptually similar to the Response class found in ASP.NET in that it can be used to send messages to the callers.
The Authors class contains two static methods named GetAuthors and GetTitlesByAuthor. As the name suggests, the GetAuthors method simply returns all the authors from the authors table in the pubs database and the GetTitlesByAuthor method returns all the titles for a specific author.
Inside the GetAuthors method, you start by getting reference to the SqlPipe object by invoking the Pipe property of the SqlContext class.
SqlPipe sp = SqlContext.Pipe;
Then you open the connection to the database using the SqlConnection object. Note that the connection string passed to the constructor of the SqlConnection object is set to "context connection=true" meaning that you want to use the context of the logged on user to open the connection to the database.
using (SqlConnection conn = new SqlConnection("context connection=true"))
Here open the connection to the database using the Open() method.
conn.Open();
Then you create an instance of the SqlCommand object and set its properties appropriately.
SqlCommand cmd = new SqlCommand();cmd.CommandType = CommandType.Text;cmd.Connection = conn;cmd.CommandText = "Select DatePart(second, GetDate()) " + " As timestamp,* from authors";
Finally you execute the sql query by calling the ExecuteReader method of the SqlCommand object.
SqlDataReader rdr = cmd.ExecuteReader();
Then using the SqlPipe object, you then return tabular results and messages to the client. This is accomplished using the Send method of the SqlPipe class.
sp.Send(rdr);
The Send method provides various overloads that are useful in transmitting data through the pipe to the calling application. Various overloads of the Send method are:
- Send (ISqlDataReader) - Sends the tabular results in the form of a SqlDataReader object.
- Send (ISqlDataRecord) - Sends the results in the form of a SqlDataRecord object.
- Send (ISqlError) - Sends error information in the form of a SqlError object.
- Send (String) - Sends messages in the form of a string value to the calling application.
Both the methods in the Authors class utilize one of the Send methods that allows you to send tabular results to the client application in the form of a SqlDataReader object. Since the GetTitlesByAuthor method implementation is very similar to the GetAuthors method, I will not be discussing that method in detail.
Now that the stored procedures are created, deploying it is very simple and straightforward. Before deploying it, you need to build the project first. To build the project, select Build->Build from the menu. This will compile all the classes in the project and if there are any compilation errors, they will be displayed in the Error List pane. Once the project is built, you can then deploy it onto the SQL Server by selecting Build->Deploy from the menu. This will not only register the assembly in the SQL Server but also deploy the stored procedures in the SQL Server. Once the stored procedures are deployed to the SQL Server, they can then be invoked from the data access layer, which is the topic of focus in the next section.
Before executing the stored procedure, ensure you execute the following sql script using SQL Server Management Studio to enable managed code execution in the SQL Server.
EXEC sp_configure 'clr enabled', 1;
RECONFIGURE WITH OVERRIDE;
GO
