目录
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。
不了解Dapper的朋友可以看这篇文章：ORM框架之Dapper简介和性能测试
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。
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 } }fObLHEIt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(@"As*SELECTs+((?:((?>((?<depth>)|)(?<-depth>)|.?)*(?(depth)(?!)))|.)*?)(?<!,s+)bFROMb", RegexOptions.IgnoreCase | RegexOptions.Multiline | RegexOptions.Singleline | RegexOptions.Compiled); public static Regex rxOrderBy = new Regex(@"bORDERs+BYs+(?!.*?(?:)|s+)ASs)(?:((?>((?<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(@"ADISTINCTs", 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
public interface IUnitOfWork : IDisposable { void SaveChanges(); } public interface IUnitOfWorkFactory { IUnitOfWork Create(); }public class UnitOfWork : IUnitOfWork { private readonly IContext _context; public UnitOfWork(IContext context) { _context = context; _context.BeginTransaction(); } public void SaveChanges() { if (!_context.IsTransactionStarted) throw new InvalidOperationException("Transaction have already been commited or disposed."); _context.Commit(); } public void Dispose() { if (_context.IsTransactionStarted) _context.Rollback(); } }public class DapperUnitOfWorkFactory : IUnitOfWorkFactory { private readonly DapperDBContext _context; public DapperUnitOfWorkFactory(DapperDBContext context) { _context = context; } public IUnitOfWork Create() { return new UnitOfWork(_context); } }定义数据仓储
#region Product public partial interface IProductRepository { Task<Product> GetAsync(int id); Task<IEnumerable<Product>> GetAllAsync(); long Insert(Product model); Task<int> InsertAsync(Product model); bool Update(Product model); Task<bool> UpdateAsync(Product model); int Count(string where, object param = null); Task<int> CountAsync(string where, object param = null); bool Exists(string where, object param = null); Task<bool> ExistsAsync(string where, object param = null); Product FirstOrDefault(string where, object param = null); Task<Product> FirstOrDefaultAsync(string where, object param = null); T FirstOrDefault<T>(string sql, object param = null); Task<T> FirstOrDefaultAsync<T>(string sql, object param = null); IEnumerable<Product> Fetch(SqlBuilder where); Task<IEnumerable<Product>> FetchAsync(SqlBuilder where); IEnumerable<T> Fetch<T>(string sql, SqlBuilder where, bool orderBy = true); Task<IEnumerable<T>> FetchAsync<T>(string sql, SqlBuilder where, bool orderBy = true); Task<Page<Product>> PageAsync(long pageIndex, long pageSize, SqlBuilder builder); Task<Page<T>> PageAsync<T>(string sql, long pageIndex, long pageSize, SqlBuilder builder); Task<SqlMapper.GridReader> QueryMultipleAsync(string sql, object param = null); } public partial class ProductRepository : IProductRepository { private readonly DapperDBContext _context; public ProductRepository(DapperDBContext context) { _context = context; } public async Task<Product> GetAsync(int id) { return await _context.GetAsync<Product>(id); } public async Task<IEnumerable<Product>> GetAllAsync() { return await _context.GetAllAsync<Product>(); } public long Insert(Product model) { return _context.Insert<Product>(model); } public async Task<int> InsertAsync(Product model) { return await _context.InsertAsync<Product>(model); } public bool Update(Product model) { return _context.Update<Product>(model); } public async Task<bool> UpdateAsync(Product model) { return await _context.UpdateAsync<Product>(model); } public int Count(string where, object param = null) { string strSql = $"SELECT COUNT(1) FROM Product {where}"; return _context.ExecuteScalar(strSql, param); } public async Task<int> CountAsync(string where, object param = null) { string strSql = $"SELECT COUNT(1) FROM Product {where}"; return await _context.ExecuteScalarAsync(strSql, param); } public bool Exists(string where, object param = null) { string strSql = $"SELECT TOP 1 1 FROM Product {where}"; var count = _context.ExecuteScalar(strSql, param); return count > 0; } public async Task<bool> ExistsAsync(string where, object param = null) { string strSql = $"SELECT TOP 1 1 FROM Product {where}"; var count = await _context.ExecuteScalarAsync(strSql, param); return count > 0; } public Product FirstOrDefault(string where, object param = null) { string strSql = $"SELECT TOP 1 * FROM Product {where}"; return _context.QueryFirstOrDefault<Product>(strSql, param); } public async Task<Product> FirstOrDefaultAsync(string where, object param = null) { string strSql = $"SELECT TOP 1 * FROM Product {where}"; return await _context.QueryFirstOrDefaultAsync<Product>(strSql, param); } public T FirstOrDefault<T>(string sql, object param = null) { return _context.QueryFirstOrDefault<T>(sql, param); } public async Task<T> FirstOrDefaultAsync<T>(string sql, object param = null) { return await _context.QueryFirstOrDefaultAsync<T>(sql, param); } public IEnumerable<Product> Fetch(SqlBuilder where) { var strSql = where.AddTemplate(@"SELECT * FROM Product /**where**/ /**orderby**/"); return _context.Query<Product>(strSql.RawSql, strSql.Parameters); } public async Task<IEnumerable<Product>> FetchAsync(SqlBuilder where) { var strSql = where.AddTemplate(@"SELECT * FROM Product /**where**/ /**orderby**/"); return await _context.QueryAsync<Product>(strSql.RawSql, strSql.Parameters); } public IEnumerable<T> Fetch<T>(string sql, SqlBuilder where, bool orderBy = true) { var _sql = orderBy ? $"{sql} /**where**/ /**orderby**/" : $"{sql} /**where**/"; var strSql = where.AddTemplate(_sql); return _context.Query<T>(strSql.RawSql, strSql.Parameters); } public async Task<IEnumerable<T>> FetchAsync<T>(string sql, SqlBuilder where, bool orderBy = true) { var _sql = orderBy ? $"{sql} /**where**/ /**orderby**/" : $"{sql} /**where**/"; var strSql = where.AddTemplate(_sql); return await _context.QueryAsync<T>(strSql.RawSql, strSql.Parameters); } public async Task<Page<Product>> PageAsync(long pageIndex, long pageSize, SqlBuilder builder) { var strSql = "SELECT * FROM Product"; return await PageAsync<Product>(strSql, pageIndex, pageSize, builder); } public async Task<Page<T>> PageAsync<T>(string sql, long pageIndex, long pageSize, SqlBuilder builder) { var strSql = builder.AddTemplate($"{sql} /**where**/ /**orderby**/"); return await _context.PageAsync<T>(pageIndex, pageSize, strSql.RawSql, strSql.Parameters); } public async Task<SqlMapper.GridReader> QueryMultipleAsync(string sql, object param = null) { return await _context.QueryMultipleAsync(sql, param); } } #endregion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; } }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：
public class ProductController : BaseController{ private readonly IProductRepository _productRepository; public ProductController( IProductRepository productRepository ) { _productRepository = productRepository; } //商品列表 [HttpGet] public async Task<IActionResult> ProductList(DateTime? startDate, DateTime? endDate, int id = 1, int productStatus = 0, string keyword = "") { var model = new ProductModels(); var builder = new Dapper.SqlBuilder(); builder.Where("ProductStatus!=@ProductStatus", new { ProductStatus = productStatus }); if (startDate.HasValue) { builder.Where("CreateTime>=@startDate", new { startDate = startDate.Value}); } if (endDate.HasValue) { builder.Where("CreateTime<@endDate", new { endDate = endDate.Value.AddDays(1)}); } if (!string.IsNullOrWhiteSpace(keyword)) { builder.Where("Name LIKE @keyword", new { keyword = $"%{StringHelper.ReplaceSql(keyword)}%" }); } builder.OrderBy("SortNum DESC,CreateTime DESC"); var list = await _productRepository.PageAsync(id, PageSize, builder); model.ProductList = new PagedList<Product>(list.Items, id, PageSize, list.TotalItems); if (Request.IsAjaxRequest()) return PartialView("_ProductList", model.ProductList); return View(model); } //添加商品 [HttpPost] public async Task<int> AddProduct(ProductModels model) { return await _productRepository.InsertAsync(model); }}public partial interface IProductService { Task<bool> AddProduct(Product productInfo, List<ProductStock> skuList); } public class ProductService: IProductService { private readonly DapperDBContext _context; private readonly IUnitOfWorkFactory _uowFactory; public ProductService(DapperDBContext context, IUnitOfWorkFactory uowFactory) { _context = context; _uowFactory = uowFactory; } /// <summary> /// 添加商品 /// </summary> /// <param name="productInfo"></param> /// <param name="skuList"></param> /// <returns></returns> public async Task<bool> AddProduct(Product productInfo, List<ProductStock> skuList) { var result = false; using (var uow = _uowFactory.Create()) { //添加产品 await _context.InsertAsync(productInfo); //添加Sku库存售价 //await _context.InsertAsync(skuList); uow.SaveChanges(); result = true; } return result; } }以上所述是小编给大家介绍的.Net Core下使用Dapper的方法，希望对大家有所帮助。在此也非常感谢大家对我们网站的支持！
