一步步實現本身的ORM（二）

時間 2019-11-17

標籤步步實現本身 orm 欄目 Java 简体版

原文原文鏈接

在第一篇《一步步實現本身的ORM（一）》裏，咱們用反射獲取類名、屬性和值，咱們用這些信息開發了簡單的INSERT方法，在上一篇文章裏咱們提到主鍵爲何沒有設置成自增加類型，單單從屬性裏咱們沒法識別哪一個是主鍵，今天咱們用Attribute來標識列，關於Attribute，引用MSDN裏描述html

MADN的定義爲：公共語言運行時容許添加相似關鍵字的描述聲明，叫作attributes, 它對程序中的元素進行標註，如類型、字段、方法和屬性等。Attributes和Microsoft .NET Framework文件的元數據（metadata）保存在一塊兒，能夠用來向運行時描述你的代碼，或者在程序運行的時候影響應用程序的行爲。咱們簡單的總結爲：定製特性attribute，本質上是一個類，其爲目標元素提供關聯附加信息，並在運行期以反射的方式來獲取附加信息。 sql

簡單來講Attribute就是描述類、方法、屬性參數等信息的。數據庫

可參考《淺析C#中的Attribute》ide

在這裏咱們定義2個Attribute，用來描述表和字段。ui

    [AttributeUsage(AttributeTargets.Class)]
    class TableAttribute : Attribute
    {
        /// <summary>
        /// 表名
        /// </summary>
        public string Name { get; private set; }

        public TableAttribute(string name)
        {
            this.Name = name;
        }
    }

    [AttributeUsage(AttributeTargets.Property)]
    class ColumnAttribute : Attribute
    {
        /// <summary>
        /// 是否爲數據庫自動生成
        /// </summary>
        public bool IsGenerated { get; set; }

        /// <summary>
        /// 列名
        /// </summary>
        public string Name { get; private set; }

        public ColumnAttribute(string name)
        {
            this.Name = name;
        }
    }

View Code

修改後的實體類以下：this

    [Table("tb_Users")]
    public class User
    {
        [Column("UserId",IsGenerated = true)]
        public int UserId { get; set; }

        [Column("Email")]
        public string Email { get; set; }

        [Column("CreatedTime")]
        public DateTime CreatedTime { get; set; }
    }

咱們把表結構也修改下spa

CREATE TABLE [dbo].[tb_Users](
    [UserId] [int] NOT NULL identity(1,1) PRIMARY KEY ,
    [Email] [nvarchar](100) NULL,
    [CreatedTime] [datetime] NULL)

下面的問題，就是咱們如何獲得表名和字段名呢？咱們仍是採用反射來實現，先獲取表名：3d

         TableAttribute[] tableAttr = (TableAttribute[])typeof(User).GetCustomAttributes(typeof(TableAttribute), true);
            if (tableAttr.Length>0)
            {
                Console.WriteLine(tableAttr[0].Name);
            }

運行結果code

再獲取列名，先查找property，而後找Attribute，代碼以下：htm

            var properties = typeof(User).GetProperties();


            for (int i = 0; i < properties.Length; i++)
            {
                var pi = properties[i];
                var columnAttrs = (ColumnAttribute[])pi.GetCustomAttributes(typeof(ColumnAttribute), true);
                if (columnAttrs.Length>0)
                {
                    Console.WriteLine("字段名：{0}，是否爲自動生成：{1}", columnAttrs[0].Name, columnAttrs[0].IsGenerated);
                }
            }

運行結果

再來修改INSERT 方法以下：

public static int Insert(User user)
        {
            var type = typeof(User);
            Dictionary<string, object> parameters = new Dictionary<string, object>();
            var properties = type.GetProperties();

            string tableName = string.Empty;
            TableAttribute[] tableAttrs = (TableAttribute[])typeof(User).GetCustomAttributes(typeof(TableAttribute), true);
            if (tableAttrs.Length > 0)
            {
                tableName = tableAttrs[0].Name;
            }
            else {
                tableName = type.Name;
            }

            /*將全部的列放到集合裏*/
            List<ColumnAttribute> columns = new List<ColumnAttribute>();
            for (int i = 0; i < properties.Length; i++)
            {
                var pi = properties[i];
                var attrs = (ColumnAttribute[])pi.GetCustomAttributes(typeof(ColumnAttribute), true);
                if (attrs.Length > 0)
                {
                    columns.Add(attrs[0]);
                }
            }


            StringBuilder sql = new StringBuilder();
            sql.Append("INSERT INTO [").Append(tableName).Append("](");
            int paramIndex = 0;

            for (int i = 0; i < properties.Length; i++)
            {
                var pi = properties[i];
                var attrs = (ColumnAttribute[])pi.GetCustomAttributes(typeof(ColumnAttribute), true);
                if (attrs.Length > 0 && attrs[0].IsGenerated == false)
                {
                    if (paramIndex > 0)
                        sql.Append(",");

                    sql.Append(attrs[0].Name);
                    paramIndex++;
                }
            }

            sql.Append(") VALUES (");
            paramIndex = 0;
            for (int i = 0; i < properties.Length; i++)
            {
                var pi = properties[i];
                var attrs = (ColumnAttribute[])pi.GetCustomAttributes(typeof(ColumnAttribute), true);
                if (attrs.Length > 0 && attrs[0].IsGenerated == false)
                {
                    if (paramIndex > 0)
                        sql.Append(",");

                    sql.Append("@p").Append(paramIndex);
                    parameters.Add("@p" + paramIndex, pi.GetValue(user, null));
                    paramIndex++;
                }
            }

            sql.Append(")");
            Console.WriteLine(sql);

            SqlConnection conn = new SqlConnection(connectionString);
            var cmd = conn.CreateCommand();
            cmd.CommandText = sql.ToString();
            foreach (var item in parameters)
            {
                var pa = cmd.CreateParameter();
                pa.ParameterName = item.Key;
                pa.Value = item.Value ?? DBNull.Value;
                cmd.Parameters.Add(pa);
            }


            conn.Open();
            return cmd.ExecuteNonQuery();
        }

View Code

運行結果

咱們再定義一個IdAttribute 類用來表示主鍵，它不須要任何屬性

    [AttributeUsage(AttributeTargets.Property)]
    class IdAttribute :ColumnAttribute
    {
        public IdAttribute(string name) : base(name)
        {
        }
    }

有了主鍵咱們下面能夠寫UPDATE和DELETE 方法：

UPDATE：

  public static int Update(User user)
        {
            var type = typeof(User);
            Dictionary<string, object> parameters = new Dictionary<string, object>();
            var properties = type.GetProperties();

            string tableName = string.Empty;
            TableAttribute[] tableAttrs = (TableAttribute[])typeof(User).GetCustomAttributes(typeof(TableAttribute), true);
            if (tableAttrs.Length > 0)
            {
                tableName = tableAttrs[0].Name;
            }
            else
            {
                tableName = type.Name;
            }

            StringBuilder sql = new StringBuilder();
            sql.Append("UPDATE [").Append(tableName).Append("] SET ");
            int paramIndex = 0;

            for (int i = 0; i < properties.Length; i++)
            {
                var pi = properties[i];
                var idAttrs = (IdAttribute[])pi.GetCustomAttributes(typeof(IdAttribute), true);
                if (idAttrs.Length > 0) //若是是主鍵 跳過
                    continue;

                var columnAttrs = (ColumnAttribute[])pi.GetCustomAttributes(typeof(ColumnAttribute), true);
                if (columnAttrs.Length > 0) 
                {
                    if (paramIndex > 0)
                        sql.Append(",");
                    // 字段 = @p
                    sql.Append(columnAttrs[0].Name).Append("=").Append("@p" + paramIndex);

                    /*參數*/
                    parameters.Add("@p" + paramIndex, pi.GetValue(user, null));
                    paramIndex++;
                }
            }

            sql.Append(" WHERE ");
            int keyIndex = 0;
            for (int i = 0; i < properties.Length; i++)
            {
                var pi = properties[i];
                var idAttrs = (IdAttribute[])pi.GetCustomAttributes(typeof(IdAttribute), true);
                if (idAttrs.Length > 0)
                {
                    if (keyIndex > 0) //考慮到有多個主鍵
                        sql.Append(" AND ");
                    sql.Append(idAttrs[0].Name).Append("=").Append("@p").Append(paramIndex);

                    /*參數*/
                    parameters.Add("@p" + paramIndex, pi.GetValue(user, null));
                    paramIndex++;
                    keyIndex++;
                }
            }
            Console.WriteLine(sql);

            SqlConnection conn = new SqlConnection(connectionString);
            var cmd = conn.CreateCommand();
            cmd.CommandText = sql.ToString();
            foreach (var item in parameters)
            {
                var pa = cmd.CreateParameter();
                pa.ParameterName = item.Key;
                pa.Value = item.Value ?? DBNull.Value;
                cmd.Parameters.Add(pa);
            }


            conn.Open();
            return cmd.ExecuteNonQuery();
        }

View Code

調用代碼：

            Update(new User()
            {
                UserId = 1,
                Email = "new@new.com",
                CreatedTime = DateTime.Now
            });

運行結果：

DELETE方法：

        public static int DeleteByKey(params object[] values)
        {
            var type = typeof(User);
            Dictionary<string, object> parameters = new Dictionary<string, object>();
            var properties = type.GetProperties();

            string tableName = string.Empty;
            TableAttribute[] tableAttrs = (TableAttribute[])typeof(User).GetCustomAttributes(typeof(TableAttribute), true);
            if (tableAttrs.Length > 0)
            {
                tableName = tableAttrs[0].Name;
            }
            else
            {
                tableName = type.Name;
            }
            
            /*將全部的列放到集合裏*/
            List<IdAttribute> columns = new List<IdAttribute>();
            for (int i = 0; i < properties.Length; i++)
            {
                var pi = properties[i];
                var attrs = (IdAttribute[])pi.GetCustomAttributes(typeof(IdAttribute), true);
                if (attrs.Length > 0)
                {
                    columns.Add(attrs[0]);
                }
            }
            if (columns.Count != values.Length)
                throw new ArgumentException("參數個數和主鍵數不一致");

            StringBuilder sql = new StringBuilder();
            sql.Append("DELETE FROM [").Append(tableName).Append("] ").Append(" WHERE ");

            for (int i = 0; i < columns.Count; i++)
            {
                if (i > 0) //考慮到有多個主鍵
                    sql.Append(" AND ");

                sql.Append(columns[i].Name).Append("=").Append("@p").Append(i);

                /*參數*/
                parameters.Add("@p" + i, values[i]);
            }
            Console.WriteLine(sql);

            SqlConnection conn = new SqlConnection(connectionString);
            var cmd = conn.CreateCommand();
            cmd.CommandText = sql.ToString();
            foreach (var item in parameters)
            {
                var pa = cmd.CreateParameter();
                pa.ParameterName = item.Key;
                pa.Value = item.Value ?? DBNull.Value;
                cmd.Parameters.Add(pa);
            }


            conn.Open();
            return cmd.ExecuteNonQuery();
        }

View Code

調用代碼：

 DeleteByKey(1);

運行結果

最後咱們把增刪改方法放在一個泛型類裏。

    class EntityHelper
    {
        private const string connectionString = "";

        public static int Insert<T>(T entity)
        {
            var type = typeof(T);
            Dictionary<string, object> parameters = new Dictionary<string, object>();
            var properties = type.GetProperties();

            string tableName = string.Empty;
            TableAttribute[] tableAttrs = (TableAttribute[])type.GetCustomAttributes(typeof(TableAttribute), true);
            if (tableAttrs.Length > 0)
            {
                tableName = tableAttrs[0].Name;
            }
            else
            {
                tableName = type.Name;
            }

            /*將全部的列放到集合裏*/
            List<ColumnAttribute> columns = new List<ColumnAttribute>();
            for (int i = 0; i < properties.Length; i++)
            {
                var pi = properties[i];
                var attrs = (ColumnAttribute[])pi.GetCustomAttributes(typeof(ColumnAttribute), true);
                if (attrs.Length > 0)
                {
                    columns.Add(attrs[0]);
                }
            }


            StringBuilder sql = new StringBuilder();
            sql.Append("INSERT INTO [").Append(tableName).Append("](");
            int paramIndex = 0;

            for (int i = 0; i < properties.Length; i++)
            {
                var pi = properties[i];
                var attrs = (ColumnAttribute[])pi.GetCustomAttributes(typeof(ColumnAttribute), true);
                if (attrs.Length > 0 && attrs[0].IsGenerated == false)
                {
                    if (paramIndex > 0)
                        sql.Append(",");

                    sql.Append(attrs[0].Name);
                    paramIndex++;
                }
            }

            sql.Append(") VALUES (");
            paramIndex = 0;
            for (int i = 0; i < properties.Length; i++)
            {
                var pi = properties[i];
                var attrs = (ColumnAttribute[])pi.GetCustomAttributes(typeof(ColumnAttribute), true);
                if (attrs.Length > 0 && attrs[0].IsGenerated == false)
                {
                    if (paramIndex > 0)
                        sql.Append(",");

                    sql.Append("@p").Append(paramIndex);
                    parameters.Add("@p" + paramIndex, pi.GetValue(entity, null));
                    paramIndex++;
                }
            }

            sql.Append(")");
            Console.WriteLine(sql);

            SqlConnection conn = new SqlConnection(connectionString);
            var cmd = conn.CreateCommand();
            cmd.CommandText = sql.ToString();
            foreach (var item in parameters)
            {
                var pa = cmd.CreateParameter();
                pa.ParameterName = item.Key;
                pa.Value = item.Value ?? DBNull.Value;
                cmd.Parameters.Add(pa);
            }


            conn.Open();
            return cmd.ExecuteNonQuery();
        }

        public static int Update<T>(T entity)
        {
            var type = typeof(T);
            Dictionary<string, object> parameters = new Dictionary<string, object>();
            var properties = type.GetProperties();

            string tableName = string.Empty;
            TableAttribute[] tableAttrs = (TableAttribute[])type.GetCustomAttributes(typeof(TableAttribute), true);
            if (tableAttrs.Length > 0)
            {
                tableName = tableAttrs[0].Name;
            }
            else
            {
                tableName = type.Name;
            }

            StringBuilder sql = new StringBuilder();
            sql.Append("UPDATE [").Append(tableName).Append("] SET ");
            int paramIndex = 0;

            for (int i = 0; i < properties.Length; i++)
            {
                var pi = properties[i];
                var idAttrs = (IdAttribute[])pi.GetCustomAttributes(typeof(IdAttribute), true);
                if (idAttrs.Length > 0) //若是是主鍵 跳過
                    continue;

                var columnAttrs = (ColumnAttribute[])pi.GetCustomAttributes(typeof(ColumnAttribute), true);
                if (columnAttrs.Length > 0)
                {
                    if (paramIndex > 0)
                        sql.Append(",");
                    // 字段 = @p
                    sql.Append(columnAttrs[0].Name).Append("=").Append("@p" + paramIndex);

                    /*參數*/
                    parameters.Add("@p" + paramIndex, pi.GetValue(entity, null));
                    paramIndex++;
                }
            }

            sql.Append(" WHERE ");
            int keyIndex = 0;
            for (int i = 0; i < properties.Length; i++)
            {
                var pi = properties[i];
                var idAttrs = (IdAttribute[])pi.GetCustomAttributes(typeof(IdAttribute), true);
                if (idAttrs.Length > 0)
                {
                    if (keyIndex > 0) //考慮到有多個主鍵
                        sql.Append(" AND ");
                    sql.Append(idAttrs[0].Name).Append("=").Append("@p").Append(paramIndex);

                    /*參數*/
                    parameters.Add("@p" + paramIndex, pi.GetValue(entity, null));
                    paramIndex++;
                    keyIndex++;
                }
            }
            Console.WriteLine(sql);

            SqlConnection conn = new SqlConnection(connectionString);
            var cmd = conn.CreateCommand();
            cmd.CommandText = sql.ToString();
            foreach (var item in parameters)
            {
                var pa = cmd.CreateParameter();
                pa.ParameterName = item.Key;
                pa.Value = item.Value ?? DBNull.Value;
                cmd.Parameters.Add(pa);
            }


            conn.Open();
            return cmd.ExecuteNonQuery();
        }

        public static int DeleteByKey<T>(params object[] values)
        {
            var type = typeof(T);
            Dictionary<string, object> parameters = new Dictionary<string, object>();
            var properties = type.GetProperties();

            string tableName = string.Empty;
            TableAttribute[] tableAttrs = (TableAttribute[])type.GetCustomAttributes(typeof(TableAttribute), true);
            if (tableAttrs.Length > 0)
            {
                tableName = tableAttrs[0].Name;
            }
            else
            {
                tableName = type.Name;
            }

            /*將全部的列放到集合裏*/
            List<IdAttribute> columns = new List<IdAttribute>();
            for (int i = 0; i < properties.Length; i++)
            {
                var pi = properties[i];
                var attrs = (IdAttribute[])pi.GetCustomAttributes(typeof(IdAttribute), true);
                if (attrs.Length > 0)
                {
                    columns.Add(attrs[0]);
                }
            }
            if (columns.Count != values.Length)
                throw new ArgumentException("參數個數和主鍵數不一致");

            StringBuilder sql = new StringBuilder();
            sql.Append("DELETE FROM [").Append(tableName).Append("] ").Append(" WHERE ");

            for (int i = 0; i < columns.Count; i++)
            {
                if (i > 0) //考慮到有多個主鍵
                    sql.Append(" AND ");

                sql.Append(columns[i].Name).Append("=").Append("@p").Append(i);

                /*參數*/
                parameters.Add("@p" + i, values[i]);
            }
            Console.WriteLine(sql);

            SqlConnection conn = new SqlConnection(connectionString);
            var cmd = conn.CreateCommand();
            cmd.CommandText = sql.ToString();
            foreach (var item in parameters)
            {
                var pa = cmd.CreateParameter();
                pa.ParameterName = item.Key;
                pa.Value = item.Value ?? DBNull.Value;
                cmd.Parameters.Add(pa);
            }


            conn.Open();
            return cmd.ExecuteNonQuery();
        }
    }

View Code

大功告成，咱們修改下調用代碼

           EntityHelper.Insert(new User()
            {
                Email = "abc@123.com",
                CreatedTime = DateTime.Now
            });

            EntityHelper.Update(new User()
            {
                UserId = 1,
                Email = "new@new.com",
                CreatedTime = DateTime.Now
            });

            EntityHelper.DeleteByKey<User>(1);

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