CPQuery SQL字符串拼接之 —— 凑热闹

昨天拜读了一下 Fish Li 的 CPQuery, 解决拼接SQL的新方法，整体上还是很赞的，提供了一种新的数据库查询方式，这让我想起了很久之前 CoolCode 写的一个字符串拼接类（StringJoiner），个人认为很不错，确实拯救了不少前同事留下来的烂代码。

 

不过，我认为 Fish Li 的代码还有一些不足之处，因为涉及的改动比较多，所以我在这里另辟一块地方，发表出来，希望 Fish Li 理解我的意思，谢谢！代码整体上借用 Fish Li 的思想，不过在一些细节问题上的处理有些不同，不多说了。上代码：

using System;

using System.Data;

using System.Data.SqlClient;

using System.Text;



namespace TestParameterJoin

{

    class Program

    {

        static void Main(string[] args)

        {

            var con = new SqlConnection();

            var cmd = con.CreateCommand();

            cmd.CommandText = "select * from table where 1 = 1";



            var builder = cmd.AsBuilder() + " and a = " + "abc" +

                                            " and b = " + 3 +

                                            " and c = " + true +

                                            " and d = " + DateTime.Now;



            // Build: select * from table where 1 = 1 and a = @p0 and b = @p1 and c = @p2 and d = @p3

            builder.Build();



            // 接着做你的数据库操作

        }

    }



    public sealed class DbCommandBuilder

    {

        private StringBuilder sbSql = new StringBuilder();

        private IDbCommand cmd = null;

        private bool isBuilded = false;



        public DbCommandBuilder(IDbCommand command)

        {

            cmd = command;

        }



        public static DbCommandBuilder operator +(DbCommandBuilder builder, string obj)

        {

            if (builder.isBuilded) throw new ApplicationException("Has builded!");



            var isParameter = obj.IndexOf('=') == -1;

            var parameterName = GetParameterName(builder);



            if (isParameter)

                builder.AppendParameter(DbType.String, () => (object)obj ?? DBNull.Value);

            else

                builder.sbSql.Append(obj).Append(parameterName);



            return builder;

        }



        public static DbCommandBuilder operator +(DbCommandBuilder builder, int? obj)

        {

            if (builder.isBuilded) throw new ApplicationException("Has builded!");



            return builder.AppendParameter(DbType.Int32, () => obj.HasValue ? (object)obj.Value : DBNull.Value);

        }



        public static DbCommandBuilder operator +(DbCommandBuilder builder, bool? obj)

        {

            if (builder.isBuilded) throw new ApplicationException("Has builded!");



            return builder.AppendParameter(DbType.Boolean, () => obj.HasValue ? (object)(obj.Value ? 1 : 0) : DBNull.Value);

        }



        public static DbCommandBuilder operator +(DbCommandBuilder builder, DateTime? obj)

        {

            if (builder.isBuilded) throw new ApplicationException("Has builded!");



            return builder.AppendParameter(DbType.DateTime, () => obj.HasValue ? (object)obj.Value : DBNull.Value);

        }



        // 这里你还可以继续添加你想要的类型



        private DbCommandBuilder AppendParameter(DbType dbType, Func<object> func)

        {

            var parameterName = GetParameterName(this);



            var param = cmd.CreateParameter();

            param.DbType = dbType;

            param.Value = func();

            param.ParameterName = parameterName;



            cmd.Parameters.Add(param);



            return this;

        }



        private static string GetParameterName(DbCommandBuilder builder)

        {

            return string.Format("@p{0}", builder.cmd.Parameters.Count);

        }



        public IDbCommand Build()

        {

            isBuilded = true;

            var sql = sbSql.ToString();

            if (!string.IsNullOrWhiteSpace(sql))

                cmd.CommandText += sql;

            return cmd;

        }



        public override string ToString()

        {

            return cmd.CommandText + (isBuilded ? string.Empty : sbSql.ToString());

        }

    }



    public static class DbCommandBuilderExtension

    {

        public static DbCommandBuilder AsBuilder(this IDbCommand cmd)

        {

            return new DbCommandBuilder(cmd);

        }

    }

}