Dapper in .Net Core

2024-01-19 14:23:28

Dapper in .Net Core - 白云任去留 - 博客园 (cnblogs.com)

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一、前言

　　关于什么是Dapper（详细入口），在此不做赘述；本文仅对Dapper在.Net Core中的使用作扼要说明，所陈代码以示例讲解为主，乃抛砖引玉，开发者可根据自身需要进行扩展和调整；其中如有疏漏之处，望不吝斧正。

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二、Dapper环境搭建

当前以.Net Core WebAPI或MVC项目为例，框架版本为.NET 5.0，相关NuGet包引用如下：

Install-Package Dapper

Install-Package Dapper.Contrib

Install-Package Dapper.SqlBuilder

Install-Package System.Data.SqlClient

其中Dapper.Contrib和Dapper.SqlBuilder为Dapper的扩展，当然，Dapper的扩展还有如Dapper.Rainbow等其他包，根据自身需要引用，对相关引用作下说明：

Dapper：不言而喻；
Dapper.Contrib：可使用对象进行数据表的增删改查，免却SQL语句的编写；
Dapper.SqlBuilder：可以方便动态构建SQL语句，如Join、SELECT、Where、OrderBy等等；
System.Data.SqlClient：由于示例数据库为Sql Server，如MySql则引用MySql.Data；

对于Dapper.Contrib实体配置选项，以Product类为例，作扼要说明如下：

[Table("Product")]
public class Product
{
    [Key]  
    public int Id { get; set; }
    public string Name{ get; set; }
    public string Description { get; set; }
    public decimal Price { get; set; }
    public DateTime CreateTime { get; set; }
}

对于实体配置项，有如下几个主要项：

Table：指定数据库表名，可忽略；
Key：指定为自动增长主键；
ExplicitKey：指定非自动增长主键，如guid；
Computed：计算列属性，Insert、Update操作将忽略此列；
Write：是否可写入，true/false，如[Write(false)]，false时Insert、Update操作将忽略此列，比如可扩展局部类作数据表额外查询字段使用；

对于数据表对象实体，可结合T4模板生成即可。

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三、Dapper封装

　　关于Dapper数据访问，这里参考Github上的某示例（入口：https://github.com/EloreTec/UnitOfWorkWithDapper），作修改调整封装如下：

定义DapperDBContext类

public abstract class DapperDBContext : IContext
    {
        private IDbConnection _connection;
        private IDbTransaction _transaction;
        private int? _commandTimeout = null;
        private readonly DapperDBContextOptions _options;

        public bool IsTransactionStarted { get; private set; }

        protected abstract IDbConnection CreateConnection(string connectionString);

        protected DapperDBContext(IOptions<DapperDBContextOptions> optionsAccessor)
        {
            _options = optionsAccessor.Value;

            _connection = CreateConnection(_options.Configuration);
            _connection.Open();

            DebugPrint("Connection started.");
        }

        #region Transaction

        public void BeginTransaction()
        {
            if (IsTransactionStarted)
                throw new InvalidOperationException("Transaction is already started.");

            _transaction = _connection.BeginTransaction();
            IsTransactionStarted = true;

            DebugPrint("Transaction started.");
        }

        public void Commit()
        {
            if (!IsTransactionStarted)
                throw new InvalidOperationException("No transaction started.");

            _transaction.Commit();
            _transaction = null;

            IsTransactionStarted = false;

            DebugPrint("Transaction committed.");
        }

        public void Rollback()
        {
            if (!IsTransactionStarted)
                throw new InvalidOperationException("No transaction started.");

            _transaction.Rollback();
            _transaction.Dispose();
            _transaction = null;

            IsTransactionStarted = false;

            DebugPrint("Transaction rollbacked and disposed.");
        }

        #endregion Transaction

        #region Dapper.Contrib.Extensions

        public async Task<T> GetAsync<T>(int id) where T : class, new()
        {
            return await _connection.GetAsync<T>(id, _transaction, _commandTimeout);
        }

        public async Task<T> GetAsync<T>(string id) where T : class, new()
        {
            return await _connection.GetAsync<T>(id, _transaction, _commandTimeout);
        }

        public async Task<IEnumerable<T>> GetAllAsync<T>() where T : class, new()
        {
            return await _connection.GetAllAsync<T>();
        }

        public long Insert<T>(T model) where T : class, new()
        {
            return _connection.Insert<T>(model, _transaction, _commandTimeout);
        }

        public async Task<int> InsertAsync<T>(T model) where T : class, new()
        {
            return await _connection.InsertAsync<T>(model, _transaction, _commandTimeout);
        }
        public bool Update<T>(T model) where T : class, new()
        {
            return _connection.Update<T>(model, _transaction, _commandTimeout);
        }

        public async Task<bool> UpdateAsync<T>(T model) where T : class, new()
        {
            return await _connection.UpdateAsync<T>(model, _transaction, _commandTimeout);          
        }

        public async Task<Page<T>> PageAsync<T>(long pageIndex, long pageSize, string sql, object param = null)
        {
            DapperPage.BuildPageQueries((pageIndex - 1) * pageSize, pageSize, sql, out string sqlCount, out string sqlPage);

            var result = new Page<T>
            {
                CurrentPage = pageIndex,
                ItemsPerPage = pageSize,
                TotalItems = await _connection.ExecuteScalarAsync<long>(sqlCount, param)
            };
            result.TotalPages = result.TotalItems / pageSize;

            if ((result.TotalItems % pageSize) != 0)
                result.TotalPages++;

            result.Items = await _connection.QueryAsync<T>(sqlPage, param);
            return result;
        }
      

        #endregion


        #region Dapper Execute & Query
      

        public int ExecuteScalar(string sql, object param = null, CommandType commandType = CommandType.Text)
        {
            return _connection.ExecuteScalar<int>(sql, param, _transaction, _commandTimeout, commandType);
        }

        public async Task<int> ExecuteScalarAsync(string sql, object param = null, CommandType commandType = CommandType.Text)
        {
            return await _connection.ExecuteScalarAsync<int>(sql, param, _transaction, _commandTimeout, commandType);
        }
        public int Execute(string sql, object param = null, CommandType commandType = CommandType.Text)
        {
            return _connection.Execute(sql, param, _transaction, _commandTimeout, commandType);
        }

        public async Task<int> ExecuteAsync(string sql, object param = null, CommandType commandType = CommandType.Text)
        {
            return await _connection.ExecuteAsync(sql, param, _transaction, _commandTimeout, commandType);
        }

        public IEnumerable<T> Query<T>(string sql, object param = null, CommandType commandType = CommandType.Text)
        {
            return _connection.Query<T>(sql, param, _transaction, true, _commandTimeout, commandType);
        }

        public async Task<IEnumerable<T>> QueryAsync<T>(string sql, object param = null, CommandType commandType = CommandType.Text)
        {
            return await _connection.QueryAsync<T>(sql, param, _transaction, _commandTimeout, commandType);
        }

        public T QueryFirstOrDefault<T>(string sql, object param = null, CommandType commandType = CommandType.Text)
        {
            return _connection.QueryFirstOrDefault<T>(sql, param, _transaction, _commandTimeout, commandType);
        }

        public async Task<T> QueryFirstOrDefaultAsync<T>(string sql, object param = null, CommandType commandType = CommandType.Text)
        {
            return await _connection.QueryFirstOrDefaultAsync<T>(sql, param, _transaction, _commandTimeout, commandType);
        }
        public IEnumerable<TReturn> Query<TFirst, TSecond, TReturn>(string sql, Func<TFirst, TSecond, TReturn> map, object param = null, string splitOn = "Id", CommandType commandType = CommandType.Text)
        {
            return _connection.Query(sql, map, param, _transaction, true, splitOn, _commandTimeout, commandType);
        }

        public async Task<IEnumerable<TReturn>> QueryAsync<TFirst, TSecond, TReturn>(string sql, Func<TFirst, TSecond, TReturn> map, object param = null, string splitOn = "Id", CommandType commandType = CommandType.Text)
        {
            return await _connection.QueryAsync(sql, map, param, _transaction, true, splitOn, _commandTimeout, commandType);
        }

        public async Task<SqlMapper.GridReader> QueryMultipleAsync(string sql, object param = null, CommandType commandType = CommandType.Text)
        {
            return await _connection.QueryMultipleAsync(sql, param, _transaction, _commandTimeout, commandType);
        }

        #endregion Dapper Execute & Query

        public void Dispose()
        {
            if (IsTransactionStarted)
                Rollback();

            _connection.Close();
            _connection.Dispose();
            _connection = null;

            DebugPrint("Connection closed and disposed.");
        }

        private void DebugPrint(string message)
        {
#if DEBUG
            Debug.Print(">>> UnitOfWorkWithDapper - Thread {0}: {1}", Thread.CurrentThread.ManagedThreadId, message);
#endif
        }
    }

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以上代码涵盖了Dapper访问数据库的基本操作，分同步和异步，其中大部分不作赘述，着重说下分页部分；

异步分页构建（PageAsync）

分页这里为方便调用，只需传入要查询的Sql语句（如：SELECT * FROM Table，必须带Order BY）、页索引、页大小即可；

至于具体如何构建的，这里参照某小型ORM工具PetaPoco，抽取相关代码如下，有兴趣的同学也可以自行改造：

public class Page<T>
    {
        /// <summary>
        /// The current page number contained in this page of result set 
        /// </summary>
        public long CurrentPage { get; set; }

        /// <summary>
        /// The total number of pages in the full result set
        /// </summary>
        public long TotalPages { get; set; }

        /// <summary>
        /// The total number of records in the full result set
        /// </summary>
        public long TotalItems { get; set; }

        /// <summary>
        /// The number of items per page
        /// </summary>
        public long ItemsPerPage { get; set; }

        /// <summary>
        /// The actual records on this page
        /// </summary>
        public IEnumerable<T> Items { get; set; }
        //public List<T> Items { get; set; }
    }
    public class DapperPage
    {
        public static void BuildPageQueries(long skip, long take, string sql, out string sqlCount, out string sqlPage)
        {
            // Split the SQL
            if (!PagingHelper.SplitSQL(sql, out PagingHelper.SQLParts parts))
                throw new Exception("Unable to parse SQL statement for paged query");

            sqlPage = BuildPageSql.BuildPageQuery(skip, take, parts);
            sqlCount = parts.sqlCount;
        }
    }

    static class BuildPageSql
    {
        public static string BuildPageQuery(long skip, long take, PagingHelper.SQLParts parts)
        {
            parts.sqlSelectRemoved = PagingHelper.rxOrderBy.Replace(parts.sqlSelectRemoved, "", 1);
            if (PagingHelper.rxDistinct.IsMatch(parts.sqlSelectRemoved))
            {
                parts.sqlSelectRemoved = "peta_inner.* FROM (SELECT " + parts.sqlSelectRemoved + ") peta_inner";
            }
            var sqlPage = string.Format("SELECT * FROM (SELECT ROW_NUMBER() OVER ({0}) peta_rn, {1}) peta_paged WHERE peta_rn>{2} AND peta_rn<={3}",
                                    parts.sqlOrderBy ?? "ORDER BY (SELECT NULL)", parts.sqlSelectRemoved, skip, skip + take);
            //args = args.Concat(new object[] { skip, skip + take }).ToArray();

            return sqlPage;
        }

        //SqlServer 2012及以上
        public static string BuildPageQuery2(long skip, long take, PagingHelper.SQLParts parts)
        {
            parts.sqlSelectRemoved = PagingHelper.rxOrderBy.Replace(parts.sqlSelectRemoved, "", 1);
            if (PagingHelper.rxDistinct.IsMatch(parts.sqlSelectRemoved))
            {
                parts.sqlSelectRemoved = "peta_inner.* FROM (SELECT " + parts.sqlSelectRemoved + ") peta_inner";
            }    

            var sqlOrderBy = parts.sqlOrderBy ?? "ORDER BY (SELECT NULL)";
            var sqlPage = $"SELECT {parts.sqlSelectRemoved} {sqlOrderBy} OFFSET {skip} ROWS FETCH NEXT {take} ROWS ONLY";
            return sqlPage;
        }
    }

    static class PagingHelper
    {
        public struct SQLParts
        {
            public string sql;
            public string sqlCount;
            public string sqlSelectRemoved;
            public string sqlOrderBy;
        }

        public static bool SplitSQL(string sql, out SQLParts parts)
        {
            parts.sql = sql;
            parts.sqlSelectRemoved = null;
            parts.sqlCount = null;
            parts.sqlOrderBy = null;

            // Extract the columns from "SELECT <whatever> FROM"
            var m = rxColumns.Match(sql);
            if (!m.Success)
                return false;

            // Save column list and replace with COUNT(*)
            Group g = m.Groups[1];
            parts.sqlSelectRemoved = sql.Substring(g.Index);

            if (rxDistinct.IsMatch(parts.sqlSelectRemoved))
                parts.sqlCount = sql.Substring(0, g.Index) + "COUNT(" + m.Groups[1].ToString().Trim() + ") " + sql.Substring(g.Index + g.Length);
            else
                parts.sqlCount = sql.Substring(0, g.Index) + "COUNT(*) " + sql.Substring(g.Index + g.Length);


            // Look for the last "ORDER BY <whatever>" clause not part of a ROW_NUMBER expression
            m = rxOrderBy.Match(parts.sqlCount);
            if (!m.Success)
            {
                parts.sqlOrderBy = null;
            }
            else
            {
                g = m.Groups[0];
                parts.sqlOrderBy = g.ToString();
                parts.sqlCount = parts.sqlCount.Substring(0, g.Index) + parts.sqlCount.Substring(g.Index + g.Length);
            }

            return true;
        }

        public static Regex rxColumns = new Regex(@"\A\s*SELECT\s+((?:\((?>\((?<depth>)|\)(?<-depth>)|.?)*(?(depth)(?!))\)|.)*?)(?<!,\s+)\bFROM\b", RegexOptions.IgnoreCase | RegexOptions.Multiline | RegexOptions.Singleline | RegexOptions.Compiled);
        public static Regex rxOrderBy = new Regex(@"\bORDER\s+BY\s+(?!.*?(?:\)|\s+)AS\s)(?:\((?>\((?<depth>)|\)(?<-depth>)|.?)*(?(depth)(?!))\)|[\w\(\)\.])+(?:\s+(?:ASC|DESC))?(?:\s*,\s*(?:\((?>\((?<depth>)|\)(?<-depth>)|.?)*(?(depth)(?!))\)|[\w\(\)\.])+(?:\s+(?:ASC|DESC))?)*", RegexOptions.RightToLeft | RegexOptions.IgnoreCase | RegexOptions.Multiline | RegexOptions.Singleline | RegexOptions.Compiled);
        public static Regex rxDistinct = new Regex(@"\ADISTINCT\s", RegexOptions.IgnoreCase | RegexOptions.Multiline | RegexOptions.Singleline | RegexOptions.Compiled);
    }

对于构建分页语句，分别示例BuildPageQuery和BuildPageQuery2，前者为通过ROW_NUMBER进行分页（针对SqlServer2005、2008），后者通过OFFSET、FETCH分页（针对SqlServer2012及以上版本），相关辅助操作类一览便知，如果使用MySql数据库，可酌情自行封装；

至于Where查询的进一步封装，有兴趣的也可兑Dapper lamada查询进行扩展。

定义工作单元与事务

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定义数据仓储

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根据自身需要进行调整或扩展，一般借助T4模板生成

数据库连接

通过Ioptions模式读取配置文件appsettings中连接字符串

public class MyDBContext : DapperDBContext
    {
        public MyDBContext(IOptions<DapperDBContextOptions> optionsAccessor) : base(optionsAccessor)
        {
        }

        protected override IDbConnection CreateConnection(string connectionString)
        {
            IDbConnection conn = new SqlConnection(connectionString);
            return conn;
        }
    }

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四、Dapper使用

Startup.cs注入并读取数据库连接字符串

{
  "SQLConnString": "Data Source=(local);Initial Catalog=database;Persist Security Info=True;User ID=sa;Password=123456;MultipleActiveResultSets=True;",  
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft": "Warning",
      "Microsoft.Hosting.Lifetime": "Information"
    }
  },
  "AllowedHosts": "*"
}

services.AddDapperDBContext<MyDBContext>(options =>
            {
                options.Configuration = Configuration["SQLConnString"];
            });

简单示例WebAPI或Net Core MVC下的调用示例：

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码农公寓

一、前言

二、Dapper环境搭建

三、Dapper封装

定义DapperDBContext类

异步分页构建（PageAsync）

定义工作单元与事务

定义数据仓储

数据库连接

四、Dapper使用

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