c# - Visual Studio 说我试图将 NULL 插入到 "id"表的 "Cars_details"记录中

Question

我正在为大学类(class)编写程序，但遇到了困难。我有 2 个表，我想用一个文本向其中插入数据。

汽车

• id INT NOT NULL PRIMARY KEY, IDENTITY(1,1)
• userId INT NOT NULL FOREIGN KEY Users(id)

Car_Details

• id INT NOT NULL PRIMARY KEY, FOREIGN KEY Cars(id)
• 名称 varchar(250) NOT NULL
• body_type VARCHAR(250) 不为空，
• fuel_type VARCHAR(250) 不为空，
• motor_power VARCHAR(250) 不为空，
• manufacture_year INT NOT NULL

意思是我正在尝试为 Car_Details 表中的 id 记录插入 NULL 值。下面我写了我的方法，我是怎么做到的。

尝试使用事务处理，但这也不起作用。

public int Insert(Record record)
{
        SqlCommand command = new SqlCommand();
        command.CommandType = System.Data.CommandType.Text;
        //command.CommandText = @"INSERT INTO Cars(userId)
        //                        VALUES ((SELECT id FROM Users WHERE id = Users.id));
        //                        INSERT INTO Car_Details(id, name, body_type, fuel_type, motor_power, manufacture_year)
        //                        VALUES ((SELECT TOP 1 id FROM Cars),@name, @body_type, @fuel_type, @motor_power, @manufacture_year);";

        command.CommandText = "SET XACT_ABORT ON BEGIN TRANSACTION DECLARE @CarID int 
  INSERT INTO Cars(userID) VALUES((SELECT id FROM Users WHERE id = Users.id))" +
            "SELECT @CarID = scope_identity()" +
            "INSERT INTO Car_Details VALUES(@CarID, @name, @body_type" + 
            "@fuel_type, @motor_power, @manufacture_year)" +
            "COMMIT";
                    //SqlParameter p_id = new SqlParameter();
                    //p_id.ParameterName = "@id";
                    //p_id.SqlDbType = System.Data.SqlDbType.Int;
                    //p_id.Direction = System.Data.ParameterDirection.Input;
                    //p_id.Value = (record as CarRecord).Id;
                    //command.Parameters.Add(p_id);

        SqlParameter p_name = new SqlParameter();
        p_name.ParameterName = "@name";
        p_name.SqlDbType = System.Data.SqlDbType.Char;
        p_name.Direction = System.Data.ParameterDirection.Input;
        p_name.Value = (record as CarRecord).Name;
        command.Parameters.Add(p_name);

        SqlParameter p_body_type = new SqlParameter();
        p_body_type.ParameterName = "@body_type";
        p_body_type.SqlDbType = System.Data.SqlDbType.VarChar;
        p_body_type.Direction = System.Data.ParameterDirection.Input;
        p_body_type.Value = (record as CarRecord).Body_type;
        command.Parameters.Add(p_body_type);

        SqlParameter p_fuel_type = new SqlParameter();
        p_fuel_type.ParameterName = "@fuel_type";
        p_fuel_type.SqlDbType = System.Data.SqlDbType.VarChar;
        p_fuel_type.Direction = System.Data.ParameterDirection.Input;
        p_fuel_type.Value = (record as CarRecord).Fuel_type;
        command.Parameters.Add(p_fuel_type);

        SqlParameter p_motor_power = new SqlParameter();
        p_motor_power.ParameterName = "@motor_power";
        p_motor_power.SqlDbType = System.Data.SqlDbType.Int;
        p_motor_power.Direction = System.Data.ParameterDirection.Input;
        p_motor_power.Value = (record as CarRecord).Motor_power;
        command.Parameters.Add(p_motor_power);

        SqlParameter p_manufactrue_year = new SqlParameter();
        p_manufactrue_year.ParameterName = "@manufacture_year";
        p_manufactrue_year.SqlDbType = System.Data.SqlDbType.Int;
        p_manufactrue_year.Direction = System.Data.ParameterDirection.Input;
        p_manufactrue_year.Value = (record as CarRecord).Manufacture_year;
        command.Parameters.Add(p_manufactrue_year);


        command.Connection = getConnection();

        int affectedRows = command.ExecuteNonQuery();
        command.Connection.Close();

        return affectedRows;
}

Answer 1

主键字段上缺少 IDENTITY (1,1) 子句。在您当前的场景中，您需要使用 IDENTITY 定义或在代码中指定您的主键值，然后将其传递给 SQL 命令。

在这里您可以找到更多信息:https://learn.microsoft.com/en-us/sql/t-sql/statements/create-table-transact-sql-identity-property?view=sql-server-2017

还有OUTPUT INSERTED.[PK列名]子句: https://www.sqlservercentral.com/articles/the-output-clause-for-insert-and-delete-statements

对于 OUTPUT 子句，您需要使用阅读器从中获取回复。

如果您正在处理未决(未提交)事务，您可能需要使用这种方法。