ado .net 学习心得

1.ado.net 概述

　　ado.net用于c#程序中的关系数据库的访问。本节代码下载地址：打开网页www.wrox.com/go/professioncsharp6 单击download code选项卡下载第37章代码。本节使用AdventureWork2014数据库。这个数据库可以从https://msftdbprodsamples.codeplex.com/中下载。另外本节代码还需引入nuget包：Microsoft.Extensions.Configuration.Json和Microsoft.Extensions.Configuration还有System.Data.SqlClient包。还有使用下述命名空间：

   

using Microsoft.Extensions.Configuration;
using System;
using System.Data;
using System.Data.SqlClient;
using static System.Console;
using System.Threading.Tasks;

2.使用数据库连接

　　a.直接使用连接串连接

　　

        public static void OpenConnection()
        {
            string connectionString = @"server=localhost\SQLEXPRESS;" +
                            "integrated security=SSPI;" +
                            "database=AdventureWorks2014";
            var connection = new SqlConnection(connectionString);

            connection.Open();

            // Do something useful
            WriteLine("connection opened");

            connection.Close();
        }    

　　

　　b.从配置文件中获取连接串

　　

        public static string GetConnectionString()
        {
            var configurationBuilder = new ConfigurationBuilder().AddJsonFile("config.json");

            IConfiguration config = configurationBuilder.Build();
            string connectionString = config["Data:DefaultConnection:ConnectionString"];
            return connectionString;
        }

　　json文件内容如下：

　　

{
	"Data": {
    "DefaultConnection": {
      "ConnectionString": "server=localhost\\SQLEXPRESS;Database=AdventureWorks2014;Trusted_Connection=True;"
    }
	}
}

　　c.数据库连接类sqlconnnection重要属性：InfoMessage和StateChange

　　每次从sqlserver 返回一个信息或警告消息，就会触发Info Message。连接状态改变时就会触发StateChange事件，代码如下：

　　

        public static void ConnectionInformation()
        {
            using (var connection = new SqlConnection(GetConnectionString()))
            {
                connection.InfoMessage += (sender, e) =>
                {
                    WriteLine($"warning or info {e.Message}");
                };
                connection.StateChange += (sender, e) =>
                {

                    WriteLine($"current state: {e.CurrentState}, before: {e.OriginalState}");
                };
                connection.Open();

                WriteLine("connection opened");
                // Do something useful

            }
        }

 3.command  命令

　　a,新建command命令有三种方式：

                    //方法一
                    var command = new SqlCommand(sql, connection);
                    //方法二
                    var command = connection.CreateCommand();
                    command.CommandText = sql;
                    //方法三
                    var command = new SqlCommand();                   
                    command.CommandText = sql;
                    command.Connection = connection;

　　其中方法二三添加一行代码可用于存储结构的执行：

　　

private static void StoredProcedure(int entityId)
        {
            using (var connection = new SqlConnection(GetConnectionString()))
            {
                SqlCommand command = connection.CreateCommand();
                command.CommandText = "[dbo].[uspGetEmployeeManagers]";
                command.CommandType = CommandType.StoredProcedure;
                SqlParameter p1 = command.CreateParameter();
                p1.SqlDbType = SqlDbType.Int;
                p1.ParameterName = "@BusinessEntityID";
                p1.Value = entityId;
                command.Parameters.Add(p1);
                connection.Open();
                using (SqlDataReader reader = command.ExecuteReader())
                {
                    while (reader.Read())
                    {
                        int recursionLevel = (int)reader["RecursionLevel"];
                        int businessEntityId = (int)reader["BusinessEntityID"];
                        string firstName = (string)reader["FirstName"];
                        string lastName = (string)reader["LastName"];
                        WriteLine($"{recursionLevel} {businessEntityId} {firstName} {lastName}");
                    }
                }
            }
        }

以及事务的执行：

　　

private static async Task TransactionSample()
        {
            using (var connection = new SqlConnection(GetConnectionString()))
            {
                await connection.OpenAsync();
                SqlTransaction tx = connection.BeginTransaction();

                try
                {
                    string sql = "INSERT INTO Sales.CreditCard (CardType, CardNumber, ExpMonth, ExpYear)" +
                        "VALUES (@CardType, @CardNumber, @ExpMonth, @ExpYear); " +
                        "SELECT SCOPE_IDENTITY()";

                    var command =connection.CreateCommand();// new SqlCommand();
                    command.CommandText = sql;
                    command.Connection = connection;
                    //执行事务
　　　　　　　　　　　　command.Transaction = tx;
                    var p1 = new SqlParameter("CardType", SqlDbType.NVarChar, 50);
                    var p2 = new SqlParameter("CardNumber", SqlDbType.NVarChar, 25);
                    var p3 = new SqlParameter("ExpMonth", SqlDbType.TinyInt);
                    var p4 = new SqlParameter("ExpYear", SqlDbType.SmallInt);
                    command.Parameters.AddRange(new SqlParameter[] { p1, p2, p3, p4 });

                    command.Parameters["CardType"].Value = "MegaWoosh";
                    command.Parameters["CardNumber"].Value = "08154711123";
                    command.Parameters["ExpMonth"].Value = 4;
                    command.Parameters["ExpYear"].Value = 2019;

                    //异步可以获取最大id
                    object id = await command.ExecuteScalarAsync();
                    WriteLine($"record added with id: {id}");

                    command.Parameters["CardType"].Value = "NeverLimits";
                    command.Parameters["CardNumber"].Value = "987654321015";
                    command.Parameters["ExpMonth"].Value = 12;
                    command.Parameters["ExpYear"].Value = 2025;


                    id = await command.ExecuteScalarAsync();
                    WriteLine($"record added with id: {id}");
                    // throw new Exception("abort");

                    tx.Commit();
                }
                catch (Exception ex)
                {
                    WriteLine($"error {ex.Message}, rolling back");
                    tx.Rollback();
                }
            }
        }

　　b.command 需要传递参数时的几种方式：

　　

switch (method) {
                case 1:
                    var productIdParamter = new SqlParameter("ProductId", SqlDbType.Int);
                    productIdParamter.Value = productId;
                    command.Parameters.Add(productIdParamter);
                    break;
                case 2:
                    command.Parameters.AddWithValue("ProductId", productId);
                    break;
                case 3:
                    command.Parameters.Add("ProductId", SqlDbType.Int);
                    command.Parameters["ProductId"].Value = productId;
                    break;
                case 4:
                    var p1 = command.CreateParameter();
                    p1.SqlDbType = SqlDbType.Int;
                    p1.ParameterName = "ProductId";
                    p1.Value = productId;
                    command.Parameters.Add(p1);
                    break;
                case 5:
                    var p2 = new SqlParameter("ProductId", SqlDbType.Int);
                    command.Parameters.Add(p2);
                    command.Parameters["ProductId"].Value = productId;
                    break;
                case 6:
                    command.Parameters.Add(new SqlParameter("ProductId", productId));
                    break;
                default:
                    command.Parameters.AddWithValue("ProdictId",productId);
                    break;                   
            }

　　3.三种command执行方法：

　　　　a.ExecuteNonQuery 返回当前操作的影响行数，可用于insert delete update

　　　　　　

public static void ExecuteNonQuery()
        {
            try
            {
                using (var connection = new SqlConnection(GetConnectionString()))
                {
                    string sql = "INSERT INTO [Sales].[SalesTerritory] ([Name], [CountryRegionCode], [Group]) " +
                        "VALUES (@Name, @CountryRegionCode, @Group)";
                    //方法一
                    //var command = new SqlCommand(sql, connection);
                    //方法二
                    //var command = connection.CreateCommand();
                    //command.CommandText = sql;
                    //方法三
                    var command = new SqlCommand();                   
                    command.CommandText = sql;
                    command.Connection = connection;

                    command.Parameters.AddWithValue("Name", "Austria16");
                    command.Parameters.AddWithValue("CountryRegionCode", "AT");
                    command.Parameters.AddWithValue("Group", "Europe1");

                    connection.Open();
                    object records = command.ExecuteNonQuery();
                    WriteLine($"{records} inserted");
                }
            }
            catch (SqlException ex)
            {
                WriteLine(ex.Message);
            }
        }

　　　　b.ExecuteScalar 返回一行一列的信息

　　　　

        private static void ExecuteScalar()
        {
            using (var connection = new SqlConnection(GetConnectionString()))
            {
                string sql = "SELECT COUNT(*) FROM Production.Product";
                SqlCommand command = connection.CreateCommand();
                command.CommandText = sql;
                connection.Open();
                object count = command.ExecuteScalar();
                WriteLine($"counted {count} product records");
            }
        }

　　　　c.ExecuteReader()方法：用于读取数据库表的多行信息。注 ：1.CommandBehavior.CloseConnection表示当command的结束对应的connection也随之关闭。2.

reader.GetInt32(0)就相当于(int)reader[0]或者（int）reader["id"]3.当reader为null时GetInt32等函数会报错

　　　　

　　private static string GetProductInformationSQL() =>
"SELECT Prod.ProductID, Prod.Name, Prod.StandardCost, Prod.ListPrice, CostHistory.StartDate, CostHistory.EndDate, CostHistory.StandardCost " +
"FROM Production.ProductCostHistory AS CostHistory " +
"INNER JOIN Production.Product AS Prod ON CostHistory.ProductId = Prod.ProductId " +
"WHERE Prod.ProductId = @ProductId";

public static void ExecuteReader(int productId)
        {
            var connection = new SqlConnection(GetConnectionString());

            string sql = GetProductInformationSQL();
            var command = new SqlCommand(sql, connection);
            SqlParameter p1 = command.CreateParameter();
            p1.SqlDbType = SqlDbType.Int;
            p1.ParameterName = "@ProductId";
            p1.Value = productId;
            command.Parameters.Add(p1);

            connection.Open();

            using (SqlDataReader reader = command.ExecuteReader(CommandBehavior.CloseConnection))
            {
                while (reader.Read())
                {
                    int id = reader.GetInt32(0);
                    string name = reader.GetString(1);
                    DateTime from = reader.GetDateTime(4);
                    DateTime? to = reader.IsDBNull(5) ? (DateTime?)null : reader.GetDateTime(5);
                    decimal standardPrice = reader.GetDecimal(6);
                    WriteLine($"{id} {name} from: {from:d} to: {to:d}; price: {standardPrice}");
                }
            }
        }

 4.异步执行办法：如通过 ReadAsync(714).wait()方式调用

        public static async Task ReadAsync(int productId)
        {
            var connection = new SqlConnection(GetConnectionString());


            string sql = GetProductInformationSQL();
            var command = new SqlCommand(sql, connection);
            var productIdParameter = new SqlParameter("ProductId", SqlDbType.Int);
            productIdParameter.Value = productId;
            command.Parameters.Add(productIdParameter);

            await connection.OpenAsync();

            using (SqlDataReader reader = await command.ExecuteReaderAsync(CommandBehavior.CloseConnection))
            {
                while (await reader.ReadAsync())
                {
                    int id = reader.GetInt32(0);
                    string name = reader.GetString(1);
                    DateTime from = reader.GetDateTime(4);
                    DateTime? to = reader.IsDBNull(5) ? (DateTime?)null : reader.GetDateTime(5);
                    decimal standardPrice = reader.GetDecimal(6);
                    WriteLine($"{id} {name} from: {from:d} to: {to:d}; price: {standardPrice}");
                }
            }
        }