ADO.NET code examples

The code listings on this page demonstrate how to retrieve data from a database by using the following ADO.NET technologies:

• ADO.NET data providers:

  • SqlClient (System.Data.SqlClient)

  • OleDb (System.Data.OleDb)

  • Odbc (System.Data.Odbc)

  • OracleClient (System.Data.OracleClient)

• ADO.NET Entity Framework:

  • LINQ to Entities

  • Typed ObjectQuery

  • EntityClient (System.Data.EntityClient)

• LINQ to SQL

ADO.NET data provider examples

The following code listings demonstrate how to retrieve data from a database using ADO.NET data providers. The data is returned in a DataReader. For more information, see Retrieving Data Using a DataReader.

SqlClient

The code in this example assumes that you can connect to the Northwind sample database on Microsoft SQL Server. The code creates a SqlCommand to select rows from the Products table, adding a SqlParameter to restrict the results to rows with a UnitPrice greater than the specified parameter value, in this case 5. The SqlConnection is opened inside a using block, which ensures that resources are closed and disposed when the code exits. The code executes the command by using a SqlDataReader, and displays the results in the console window. If you're using System.Data.SqlClient, you should consider upgrading to Microsoft.Data.SqlClient as it's where future investments and new feature developments are being made. For more information, see Introducing the new Microsoft.Data.SqlClient.

ข้อสำคัญ

Microsoft recommends that you use the most secure authentication flow available. If you're connecting to Azure SQL, Managed Identities for Azure resources is the recommended authentication method.

C#

using System;
using System.Data.SqlClient;

static class Program
{
    static void Main()
    {
        const string connectionString =
            "Data Source=(local);Initial Catalog=Northwind;"
            + "Integrated Security=true";

        // Provide the query string with a parameter placeholder.
        const string queryString =
            "SELECT ProductID, UnitPrice, ProductName from dbo.products "
                + "WHERE UnitPrice > @pricePoint "
                + "ORDER BY UnitPrice DESC;";

        // Specify the parameter value.
        const int paramValue = 5;

        // Create and open the connection in a using block. This
        // ensures that all resources will be closed and disposed
        // when the code exits.
        using (SqlConnection connection =
            new(connectionString))
        {
            // Create the Command and Parameter objects.
            SqlCommand command = new(queryString, connection);
            command.Parameters.AddWithValue("@pricePoint", paramValue);

            // Open the connection in a try/catch block.
            // Create and execute the DataReader, writing the result
            // set to the console window.
            try
            {
                connection.Open();
                SqlDataReader reader = command.ExecuteReader();
                while (reader.Read())
                {
                    Console.WriteLine("\t{0}\t{1}\t{2}",
                        reader[0], reader[1], reader[2]);
                }
                reader.Close();
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }
            Console.ReadLine();
        }
    }

OleDb

The code in this example assumes that you can connect to the Microsoft Access Northwind sample database. The code creates a OleDbCommand to select rows from the Products table, adding a OleDbParameter to restrict the results to rows with a UnitPrice greater than the specified parameter value, in this case 5. The OleDbConnection is opened inside of a using block, which ensures that resources are closed and disposed when the code exits. The code executes the command by using a OleDbDataReader, and displays the results in the console window.

C#

using System;
using System.Data.OleDb;
using System.Runtime.Versioning;

// API is only supported on Windows
[SupportedOSPlatform("windows")]
static class Program
{
    static void Main()
    {
        const string connectionString =
        "Provider=Microsoft.Jet.OLEDB.4.0;Data Source="
            + "c:\\Data\\Northwind.mdb;...";

        // Provide the query string with a parameter placeholder.
        const string queryString =
            "SELECT ProductID, UnitPrice, ProductName from products "
                + "WHERE UnitPrice > ? "
                + "ORDER BY UnitPrice DESC;";

        // Specify the parameter value.
        const int paramValue = 5;

        // Create and open the connection in a using block. This
        // ensures that all resources will be closed and disposed
        // when the code exits.
        using (OleDbConnection connection =
            new(connectionString))
        {
            // Create the Command and Parameter objects.
            OleDbCommand command = new(queryString, connection);
            command.Parameters.AddWithValue("@pricePoint", paramValue);

            // Open the connection in a try/catch block.
            // Create and execute the DataReader, writing the result
            // set to the console window.
            try
            {
                connection.Open();
                OleDbDataReader reader = command.ExecuteReader();
                while (reader.Read())
                {
                    Console.WriteLine("\t{0}\t{1}\t{2}",
                        reader[0], reader[1], reader[2]);
                }
                reader.Close();
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }
            Console.ReadLine();
        }
    }

Odbc

The code in this example assumes that you can connect to the Microsoft Access Northwind sample database. The code creates a OdbcCommand to select rows from the Products table, adding a OdbcParameter to restrict the results to rows with a UnitPrice greater than the specified parameter value, in this case 5. The OdbcConnection is opened inside a using block, which ensures that resources are closed and disposed when the code exits. The code executes the command by using a OdbcDataReader, and displays the results in the console window.

C#

using System;
using System.Data.Odbc;

static class Program
{
    static void Main()
    {
        const string connectionString =
            "Driver={Microsoft Access Driver (*.mdb)};...";

        // Provide the query string with a parameter placeholder.
        const string queryString =
            "SELECT ProductID, UnitPrice, ProductName from products "
                + "WHERE UnitPrice > ? "
                + "ORDER BY UnitPrice DESC;";

        // Specify the parameter value.
        const int paramValue = 5;

        // Create and open the connection in a using block. This
        // ensures that all resources will be closed and disposed
        // when the code exits.
        using (OdbcConnection connection =
            new(connectionString))
        {
            // Create the Command and Parameter objects.
            OdbcCommand command = new(queryString, connection);
            command.Parameters.AddWithValue("@pricePoint", paramValue);

            // Open the connection in a try/catch block.
            // Create and execute the DataReader, writing the result
            // set to the console window.
            try
            {
                connection.Open();
                OdbcDataReader reader = command.ExecuteReader();
                while (reader.Read())
                {
                    Console.WriteLine("\t{0}\t{1}\t{2}",
                        reader[0], reader[1], reader[2]);
                }
                reader.Close();
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }
            Console.ReadLine();
        }
    }
}

OracleClient

The code in this example assumes a connection to DEMO.CUSTOMER on an Oracle server. You must also add a reference to the System.Data.OracleClient.dll. The code returns the data in an OracleDataReader.

ข้อสำคัญ

Microsoft recommends that you use the most secure authentication flow available. If you're connecting to Azure SQL, Managed Identities for Azure resources is the recommended authentication method.

C#

using System;
using System.Data.OracleClient;

static class Program
{
    static void Main()
    {
        const string connectionString =
            "Data Source=ThisOracleServer;Integrated Security=yes;";
        const string queryString =
            "SELECT CUSTOMER_ID, NAME FROM DEMO.CUSTOMER";
        using (OracleConnection connection =
                   new(connectionString))
        {
            OracleCommand command = connection.CreateCommand();
            command.CommandText = queryString;

            try
            {
                connection.Open();

                OracleDataReader reader = command.ExecuteReader();

                while (reader.Read())
                {
                    Console.WriteLine("\t{0}\t{1}",
                        reader[0], reader[1]);
                }
                reader.Close();
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }
        }
    }
}

Entity Framework examples

The following code listings demonstrate how to retrieve data from a data source by querying entities in an Entity Data Model (EDM). These examples use a model based on the Northwind sample database. For more information about Entity Framework, see Entity Framework Overview.

LINQ to Entities

The code in this example uses a LINQ query to return data as Categories objects, which are projected as an anonymous type that contains only the CategoryID and CategoryName properties. For more information, see LINQ to Entities Overview.

C#

using System;
using System.Linq;
using System.Data.Objects;
using NorthwindModel;

class LinqSample
{
    public static void ExecuteQuery()
    {
        using (NorthwindEntities context = new NorthwindEntities())
        {
            try
            {
                var query = from category in context.Categories
                            select new
                            {
                                categoryID = category.CategoryID,
                                categoryName = category.CategoryName
                            };

                foreach (var categoryInfo in query)
                {
                    Console.WriteLine("\t{0}\t{1}",
                        categoryInfo.categoryID, categoryInfo.categoryName);
                }
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }
        }
    }
}

Typed ObjectQuery

The code in this example uses an ObjectQuery<T> to return data as Categories objects. For more information, see Object Queries.

C#

using System;
using System.Data.Objects;
using NorthwindModel;

class ObjectQuerySample
{
    public static void ExecuteQuery()
    {
        using (NorthwindEntities context = new NorthwindEntities())
        {
            ObjectQuery<Categories> categoryQuery = context.Categories;

            foreach (Categories category in
                categoryQuery.Execute(MergeOption.AppendOnly))
            {
                Console.WriteLine("\t{0}\t{1}",
                    category.CategoryID, category.CategoryName);
            }
        }
    }
}

EntityClient

The code in this example uses an EntityCommand to execute an Entity SQL query. This query returns a list of records that represent instances of the Categories entity type. An EntityDataReader is used to access data records in the result set. For more information, see EntityClient Provider for the Entity Framework.

C#

using System;
using System.Data;
using System.Data.Common;
using System.Data.EntityClient;
using NorthwindModel;

class EntityClientSample
{
    public static void ExecuteQuery()
    {
        string queryString =
            @"SELECT c.CategoryID, c.CategoryName
                FROM NorthwindEntities.Categories AS c";

        using (EntityConnection conn =
            new EntityConnection("name=NorthwindEntities"))
        {
            try
            {
                conn.Open();
                using (EntityCommand query = new EntityCommand(queryString, conn))
                {
                    using (DbDataReader rdr =
                        query.ExecuteReader(CommandBehavior.SequentialAccess))
                    {
                        while (rdr.Read())
                        {
                            Console.WriteLine("\t{0}\t{1}", rdr[0], rdr[1]);
                        }
                    }
                }
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.Message);
            }
        }
    }
}

LINQ to SQL

The code in this example uses a LINQ query to return data as Categories objects, which are projected as an anonymous type that contains only the CategoryID and CategoryName properties. This example is based on the Northwind data context. For more information, see Getting Started.

C#

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Northwind;

    class LinqSqlSample
    {
        public static void ExecuteQuery()
        {
            using (NorthwindDataContext db = new NorthwindDataContext())
            {
                try
                {
                    var query = from category in db.Categories
                                select new
                                {
                                    categoryID = category.CategoryID,
                                    categoryName = category.CategoryName
                                };

                    foreach (var categoryInfo in query)
                    {
                        Console.WriteLine("vbTab {0} vbTab {1}",
                            categoryInfo.categoryID, categoryInfo.categoryName);
                    }
                }
                catch (Exception ex)
                {
                    Console.WriteLine(ex.Message);
                }
            }
        }
    }

See also

• ADO.NET Overview
• Retrieving and Modifying Data in ADO.NET
• Creating Data Applications
• Querying an Entity Data Model (Entity Framework Tasks)
• How to: Execute a Query that Returns Anonymous Type Objects