Working with SQL Server Functions and .NET

By:Artemakis Artemiou | Last Updated: 2018-12-13 || Related Tips:More > Application Development Problem

In previous .NET Application Development tips , we've learned how to get started with .NET and SQL Server data access. To this end, we've learned how to connect to SQL Server from a C# program and run a simple query, as well as how to query SQL Server tables from .NET and process the results. Moreover, we've learned how to work with SQL Server stored procedures from within .NET applications. In this tip, we continue this journey and we will learn how to work with SQL Server functions from within a .NET Application.

Solution

There is more than one type of SQL Server function. Currently, in SQL Server 2017, the function types are:

Table-valued Functions Scalar-valued Functions Aggregate Functions System Functions

In this tip, we are going to see 3 different examples of calling 3 of the above types of SQL Server functions from within our .NET application. Note that we won't examine Aggregate Functions, because we would need to create a CLR assembly for this, which is something that will be covered in a future tip.

Sample Database

Just like in my previous tips, all examples will be based on the database " SampleDB " which can be found on a test SQL Server 2017 named instance on my local machine, which is called " SQL2K17 ".

Here's a screenshot of the SQL Server instance, as it can be seen in SSMS:

The sample database has two tables named " employees " and " location ", as well as the below two user-defined functions:

fnGetEmployeeInfo (table-valued function) fnGetTotalEmployees (scalar-valued function)

Let's take a look at their DDL script:

Function "fnGetEmployeeInfo" DDL Script: USE [SampleDB]
GO
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE FUNCTION [dbo].[fnGetEmployeeInfo]
(
@empID INT
)
RETURNS TABLE
AS
RETURN
(
SELECT e.id,
e.code,
e.firstName,
e.lastName,
e.locationID,
l.code AS locationCode,
l.descr AS localDescr
FROM dbo.employees e
INNER JOIN dbo.location l
ON l.id = e.locationID
WHERE e.id=@empID
);
GO Function "fnGetTotalEmployees" DDL Script: USE [SampleDB]
GO
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE FUNCTION [dbo].[fnGetTotalEmployees]
(
@locationID INT
)
RETURNS INT
AS
BEGIN
DECLARE @result INT
SELECT @result=(SELECT COUNT(*) FROM dbo.employees WHERE locationID=@locationID);
-- Return the result of the function
RETURN @result
END
GO

The fnGetEmployeeInfo function, takes as an input parameter the employee ID and returns employee-related information.

The fnGetTotalEmployees function, takes an input parameter the location ID and returns the number of all employees for the specific location.

We will use the above two functions in our examples, as well as the system function " GETDATE() ".

The system function " GETDATE() ", as the name implies, returns the current date and time.

Sample Data

The sample database has two tables named "employees" and "location". In the below screenshot, you can take a look at the data currently stored in these two tables.

Calling the SQL Server Functions from a .NET Application

The next step in our example, is to write a .NET application, preferable in C#, that connects to the database server and properly calls the 3 functions.

This example, is based on the examples originally presented in my previous .NET Application Development tips .

One of the main points, again like in the case of stored procedures, is that I will make use of the .NET Class SqlParameter in order to write more secure code, thus minimizing the risk for SQL injections.

Connecting to the SQL Server Instance Connection String

This is my connection string:

string connString = @"Server =.\SQL2K17; Database = SampleDB; Trusted_Connection = True;";

Using the above connection string, I will connect to the named instance "SQL2K17" on the local machine, using a trusted connection, that is, with my windows account.

Calling SQL Server Function "fnGetEmployeeInfo"

In the below code example, I'm presenting the full .NET code for a C# console application that calls the function "fnGetEmployeeInfo" and process the results.

Note:Prior to start writing the code, similarly to my previous tips on .NET Application Development , you will need to create a new Visual C# project in Visual Studio, and select the "Console App (.NET Framework)" template. In my example, I named the project " TestApp4 " and saved it in the "C:\temp\demos" folder on my local machine (a new subfolder with the name of the project was created).

Here's the code:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Data.SqlClient;
using System.Data;
namespace TestApp4
{
class Program
{
static void Main(string[] args)
{
//set the connection string
string connString = @"Server =.\SQL2K17; Database = SampleDB; Trusted_Connection = True;";
//variables to store the query results
int empID, locationID;
string empCode, empFirstName, empLastName, locationCode, locationDescr;
try
{
//sql connection object
using (SqlConnection conn = new SqlConnection(connString))
{
//define the query text
string query = @"SELECT * FROM [dbo].[fnGetEmployeeInfo](@empID);";
//define the SqlCommand object
SqlCommand cmd = new SqlCommand(query, conn);
//parameter value will be set from command line
SqlParameter param1 = new SqlParameter();
param1.ParameterName = "@empID";
param1.SqlDbType = SqlDbType.Int;
param1.Value = int.Parse(args[0].ToString());
//pass parameter to the SQL Command
cmd.Parameters.Add(param1);
//open connection
conn.Open();
//execute the SQLCommand
SqlDataReader dr = cmd.ExecuteReader();
Console.WriteLine(Environment.NewLine + "Retrieving data from database..." + Environment.NewLine);
Co