应用程序框架实战二十六:查询对象

信息系统的查询需求千变万化，在仓储中为每个查询需求创建一个特殊方法，将导致大量乏味而臃肿的接口。

一种更加可行的办法是，在应用层服务中描述查询需求，并通过仓储执行查询。

为了能够更好的描述查询需求，可以将查询功能从仓储中抽取出来，专门创建一个查询对象。

查询最复杂的部分是条件过滤，这也是查询对象的主要职责。查询对象可以认为是规约模式的一个变种，允许查询对象动态创建查询条件。

在Util.Domains项目Repositories目录中，创建查询对象基接口IQueryBase，代码如下。

using System; using System.Linq.Expressions; namespace Util.Domains.Repositories {  /// <summary>  /// 查询对象  /// </summary>  /// <typeparam name="TEntity">实体类型</typeparam>  public interface IQueryBase<TEntity> : IPager where TEntity : class, IAggregateRoot {   /// <summary>   /// 获取谓词   /// </summary>   Expression<Func<TEntity, bool>> GetPredicate();   /// <summary>   /// 获取排序   /// </summary>   string GetOrderBy();  } } 

IQueryBase接口主要用来支持将查询对象传入仓储中。

在仓储接口IRepository中增加两个方法，代码如下。

 /// <summary>  /// 查询  /// </summary>  /// <param name="query">查询对象</param>  IQueryable<TEntity> Query( IQueryBase<TEntity> query );  /// <summary>  /// 分页查询  /// </summary>  /// <param name="query">查询对象</param>  PagerList<TEntity> PagerQuery( IQueryBase<TEntity> query ); 

在仓储类Repository中实现这两个方法，代码如下。

 /// <summary>  /// 查询  /// </summary>  /// <param name="query">查询对象</param>  public IQueryable<TEntity> Query( IQueryBase<TEntity> query ) {      return FilterBy( Find(), query );  }  /// <summary>  /// 过滤  /// </summary>  protected IQueryable<TEntity> FilterBy( IQueryable<TEntity> queryable, IQueryBase<TEntity> query ) {      var predicate = query.GetPredicate();      if ( predicate == null )   return queryable;      return queryable.Where( predicate );  }  /// <summary>  /// 分页查询  /// </summary>  /// <param name="query">查询对象</param>  public virtual PagerList<TEntity> PagerQuery( IQueryBase<TEntity> query ) {      return Query( query ).PagerResult( query );  } 

以上代码完成了将查询对象传入仓储并获取结果，下面开始实现查询对象。

在Util.Datas项目Queries目录中，创建IQuery接口，代码如下。

using System; using System.Collections.Generic; using System.Linq; using System.Linq.Expressions; using Util.Domains; using Util.Domains.Repositories; namespace Util.Datas.Queries {     /// <summary>     /// 查询对象     /// </summary>     /// <typeparam name="TEntity">实体类型</typeparam>     /// <typeparam name="TKey">实体标识类型</typeparam>     public interface IQuery<TEntity, TKey> : IQueryBase<TEntity> where TEntity : class,IAggregateRoot<TKey> {  /// <summary>  /// 添加谓词,仅能添加一个条件,如果参数值为空，则忽略该条件  /// </summary>  /// <param name="predicate">谓词</param>  /// <param name="isOr">是否使用Or连接</param>  IQuery<TEntity, TKey> Filter( Expression<Func<TEntity, bool>> predicate, bool isOr = false );  /// <summary>  /// 过滤条件  /// </summary>  /// <param name="propertyName">属性名</param>  /// <param name="value">值</param>  /// <param name="operator">运算符</param>  IQuery<TEntity,TKey> Filter( string propertyName, object value, Operator @operator = Operator.Equal );  /// <summary>  /// 添加查询条件  /// </summary>  /// <param name="criteria">查询条件</param>  IQuery<TEntity,TKey> Filter( ICriteria<TEntity> criteria );  /// <summary>  /// 过滤int数值段  /// </summary>  /// <typeparam name="TProperty">属性类型</typeparam>  /// <param name="propertyExpression">属性表达式，范例：t => t.Age</param>  /// <param name="min">最小值</param>  /// <param name="max">最大值</param>  IQuery<TEntity,TKey> FilterInt<TProperty>( Expression<Func<TEntity, TProperty>> propertyExpression, int? min,int? max );  /// <summary>  /// 过滤double数值段  /// </summary>  /// <typeparam name="TProperty">属性类型</typeparam>  /// <param name="propertyExpression">属性表达式，范例：t => t.Age</param>  /// <param name="min">最小值</param>  /// <param name="max">最大值</param>  IQuery<TEntity,TKey> FilterDouble<TProperty>( Expression<Func<TEntity, TProperty>> propertyExpression, double? min,      double? max );  /// <summary>  /// 过滤日期段，不包含时间  /// </summary>  /// <typeparam name="TProperty">属性类型</typeparam>  /// <param name="propertyExpression">属性表达式，范例：t => t.Age</param>  /// <param name="min">最小值</param>  /// <param name="max">最大值</param>  IQuery<TEntity,TKey> FilterDate<TProperty>( Expression<Func<TEntity, TProperty>> propertyExpression, DateTime? min,      DateTime? max );  /// <summary>  /// 过滤日期时间段，包含时间  /// </summary>  /// <typeparam name="TProperty">属性类型</typeparam>  /// <param name="propertyExpression">属性表达式，范例：t => t.Age</param>  /// <param name="min">最小值</param>  /// <param name="max">最大值</param>  IQuery<TEntity,TKey> FilterDateTime<TProperty>( Expression<Func<TEntity, TProperty>> propertyExpression,      DateTime? min, DateTime? max );  /// <summary>  /// 过滤decimal数值段  /// </summary>  /// <typeparam name="TProperty">属性类型</typeparam>  /// <param name="propertyExpression">属性表达式，范例：t => t.Age</param>  /// <param name="min">最小值</param>  /// <param name="max">最大值</param>  IQuery<TEntity,TKey> FilterDecimal<TProperty>( Expression<Func<TEntity, TProperty>> propertyExpression, decimal? min,      decimal? max );  /// <summary>  /// 与连接,将传入的查询条件合并到当前对象  /// </summary>  /// <param name="query">查询对象</param>  IQuery<TEntity,TKey> And( IQuery<TEntity,TKey> query );  /// <summary>  /// 与连接,将传入的查询条件合并到当前对象  /// </summary>  /// <param name="predicate">谓词</param>  IQuery<TEntity,TKey> And( Expression<Func<TEntity, bool>> predicate );  /// <summary>  /// 或连接,将传入的查询条件合并到当前对象  /// </summary>  /// <param name="query">查询对象</param>  IQuery<TEntity,TKey> Or( IQuery<TEntity,TKey> query );  /// <summary>  /// 或连接,将传入的查询条件合并到当前对象  /// </summary>  /// <param name="predicate">谓词</param>  IQuery<TEntity,TKey> Or( Expression<Func<TEntity, bool>> predicate );  /// <summary>  /// 添加排序，支持多次调用OrderBy创建多级排序  /// </summary>  /// <typeparam name="TProperty">属性类型</typeparam>  /// <param name="expression">属性表达式</param>  /// <param name="desc">是否降序</param>  IQuery<TEntity,TKey> OrderBy<TProperty>( Expression<Func<TEntity, TProperty>> expression, bool desc = false );  /// <summary>  /// 添加排序，支持多次调用OrderBy创建多级排序  /// </summary>  /// <param name="propertyName">排序属性</param>  /// <param name="desc">是否降序</param>  IQuery<TEntity,TKey> OrderBy( string propertyName, bool desc = false );  /// <summary>  /// 获取列表  /// </summary>  /// <param name="queryable">数据源</param>  List<TEntity> GetList( IQueryable<TEntity> queryable );  /// <summary>  /// 获取分页列表  /// </summary>  /// <param name="queryable">数据源</param>  PagerList<TEntity> GetPagerList( IQueryable<TEntity> queryable );     } } 

查询对象中定义的过滤方法默认都是以And方式连接，所以需要增加专门的Or连接方法。当查询需求比较复杂时，可以创建多个查询对象进行合并，从而创建更为复杂的查询条件。

为了使用方便，查询对象本身还提供了获取数据的方法，需要传入IQueryable 对象，以便执行实际的查询操作。

在Util.Datas项目Queries目录中，创建查询对象实现类Query，代码如下。

using System; using System.Collections.Generic; using System.Linq; using System.Linq.Expressions; using Util.Datas.Queries.Criterias; using Util.Datas.Queries.OrderBys; using Util.Domains; using Util.Domains.Repositories; namespace Util.Datas.Queries {     /// <summary>     /// 查询对象     /// </summary>     /// <typeparam name="TEntity">实体类型</typeparam>     /// <typeparam name="TKey">实体标识类型</typeparam>     public class Query<TEntity, TKey> : Pager, IQuery<TEntity, TKey> where TEntity : class ,IAggregateRoot<TKey> {  #region 构造方法  /// <summary>  /// 初始化查询对象  /// </summary>  public Query() {      OrderBuilder = new OrderByBuilder();  }  /// <summary>  /// 初始化查询对象  /// </summary>  /// <param name="pager">分页对象</param>  public Query( IPager pager ) : this() {      Page = pager.Page;      PageSize = pager.PageSize;      TotalCount = pager.TotalCount;      OrderBy( pager.Order );  }  #endregion  #region 属性  /// <summary>  /// 查询条件  /// </summary>  private ICriteria<TEntity> Criteria { get; set; }  /// <summary>  /// 排序生成器  /// </summary>  private OrderByBuilder OrderBuilder { get; set; }  #endregion  #region GetPredicate(获取谓词)  /// <summary>  /// 获取谓词  /// </summary>  public Expression<Func<TEntity, bool>> GetPredicate() {      if ( Criteria == null )   return null;      return Criteria.GetPredicate();  }  #endregion  #region GetOrderBy(获取排序)  /// <summary>  /// 获取排序  /// </summary>  public string GetOrderBy() {      Order = OrderBuilder.Generate();      if ( string.IsNullOrWhiteSpace( Order ) )   Order = "Id desc";      return Order;  }  #endregion  #region 过滤条件  /// <summary>  /// 添加谓词,仅能添加一个条件,如果参数值为空，则忽略该条件  /// </summary>  /// <param name="predicate">谓词</param>  /// <param name="isOr">是否使用Or连接</param>  public IQuery<TEntity, TKey> Filter( Expression<Func<TEntity, bool>> predicate,bool isOr = false ) {      predicate = QueryHelper.ValidatePredicate( predicate );      if ( predicate == null )   return this;      if ( isOr )   Or( predicate );      else    And( predicate );      return this;  }  /// <summary>  /// 过滤条件  /// </summary>  /// <param name="propertyName">属性名</param>  /// <param name="value">值</param>  /// <param name="operator">运算符</param>  public IQuery<TEntity, TKey> Filter( string propertyName, object value, Operator @operator = Operator.Equal ) {      return Filter( Lambda.ParsePredicate<TEntity>( propertyName, value, @operator ) );  }  /// <summary>  /// 添加查询条件  /// </summary>  /// <param name="criteria">查询条件</param>  public IQuery<TEntity, TKey> Filter( ICriteria<TEntity> criteria ) {      And( criteria.GetPredicate() );      return this;  }  /// <summary>  /// 过滤int数值段  /// </summary>  /// <typeparam name="TProperty">属性类型</typeparam>  /// <param name="propertyExpression">属性表达式，范例：t => t.Age</param>  /// <param name="min">最小值</param>  /// <param name="max">最大值</param>  public IQuery<TEntity, TKey> FilterInt<TProperty>( Expression<Func<TEntity, TProperty>> propertyExpression, int? min, int? max ) {      return Filter( new IntSegmentCriteria<TEntity, TProperty>( propertyExpression, min, max ) );  }  /// <summary>  /// 过滤double数值段  /// </summary>  /// <typeparam name="TProperty">属性类型</typeparam>  /// <param name="propertyExpression">属性表达式，范例：t => t.Age</param>  /// <param name="min">最小值</param>  /// <param name="max">最大值</param>  public IQuery<TEntity, TKey> FilterDouble<TProperty>( Expression<Func<TEntity, TProperty>> propertyExpression, double? min, double? max ) {      return Filter( new DoubleSegmentCriteria<TEntity, TProperty>( propertyExpression, min, max ) );  }  /// <summary>  /// 过滤日期段，不包含时间  /// </summary>  /// <typeparam name="TProperty">属性类型</typeparam>  /// <param name="propertyExpression">属性表达式，范例：t => t.Age</param>  /// <param name="min">最小值</param>  /// <param name="max">最大值</param>  public IQuery<TEntity, TKey> FilterDate<TProperty>( Expression<Func<TEntity, TProperty>> propertyExpression, DateTime? min, DateTime? max ) {      return Filter( new DateSegmentCriteria<TEntity, TProperty>( propertyExpression, min, max ) );  }  /// <summary>  /// 过滤日期时间段，包含时间  /// </summary>  /// <typeparam name="TProperty">属性类型</typeparam>  /// <param name="propertyExpression">属性表达式，范例：t => t.Age</param>  /// <param name="min">最小值</param>  /// <param name="max">最大值</param>  public IQuery<TEntity, TKey> FilterDateTime<TProperty>( Expression<Func<TEntity, TProperty>> propertyExpression, DateTime? min, DateTime? max ) {      return Filter( new DateTimeSegmentCriteria<TEntity, TProperty>( propertyExpression, min, max ) );  }  /// <summary>  /// 过滤decimal数值段  /// </summary>  /// <typeparam name="TProperty">属性类型</typeparam>  /// <param name="propertyExpression">属性表达式，范例：t => t.Age</param>  /// <param name="min">最小值</param>  /// <param name="max">最大值</param>  public IQuery<TEntity, TKey> FilterDecimal<TProperty>( Expression<Func<TEntity, TProperty>> propertyExpression, decimal? min, decimal? max ) {      return Filter( new DecimalSegmentCriteria<TEntity, TProperty>( propertyExpression, min, max ) );  }  #endregion  #region 连接  /// <summary>  /// 与连接,将传入的查询条件合并到当前对象  /// </summary>  /// <param name="query">查询对象</param>  public IQuery<TEntity, TKey> And( IQuery<TEntity, TKey> query ) {      return And( query.GetPredicate() );  }  /// <summary>  /// 与连接,将传入的查询条件合并到当前对象  /// </summary>  /// <param name="predicate">谓词</param>  public IQuery<TEntity, TKey> And( Expression<Func<TEntity, bool>> predicate ) {      if ( Criteria == null ) {   Criteria = new Criteria<TEntity>( predicate );   return this;      }      Criteria = new AndCriteria<TEntity>( Criteria.GetPredicate(), predicate );      return this;  }  /// <summary>  /// 或连接,将传入的查询条件合并到当前对象  /// </summary>  /// <param name="query">查询对象</param>  public IQuery<TEntity, TKey> Or( IQuery<TEntity, TKey> query ) {      return Or( query.GetPredicate() );  }  /// <summary>  /// 或连接,将传入的查询条件合并到当前对象  /// </summary>  /// <param name="predicate">谓词</param>  public IQuery<TEntity, TKey> Or( Expression<Func<TEntity, bool>> predicate ) {      if ( Criteria == null ) {   Criteria = new Criteria<TEntity>( predicate );   return this;      }      Criteria = new OrCriteria<TEntity>( Criteria.GetPredicate(), predicate );      return this;  }  #endregion  #region OrderBy(排序)  /// <summary>  /// 添加排序，支持多次调用OrderBy创建多级排序  /// </summary>  /// <typeparam name="TProperty">属性类型</typeparam>  /// <param name="expression">属性表达式</param>  /// <param name="desc">是否降序</param>  public IQuery<TEntity, TKey> OrderBy<TProperty>( Expression<Func<TEntity, TProperty>> expression, bool desc = false ) {      return OrderBy( Lambda.GetName( expression ), desc );  }  /// <summary>  /// 添加排序，支持多次调用OrderBy创建多级排序  /// </summary>  /// <param name="propertyName">排序属性</param>  /// <param name="desc">是否降序</param>  public IQuery<TEntity, TKey> OrderBy( string propertyName, bool desc = false ) {      OrderBuilder.Add( propertyName, desc );      GetOrderBy();      return this;  }  #endregion  #region Clear(清理)  /// <summary>  /// 清理  /// </summary>  public void Clear() {      Criteria = null;      OrderBuilder = new OrderByBuilder();  }  #endregion  #region GetList(获取列表)  /// <summary>  /// 获取列表  /// </summary>  /// <param name="queryable">数据源</param>  public List<TEntity> GetList( IQueryable<TEntity> queryable ) {      return Execute( queryable ).OrderBy( Order ).ToList();  }  /// <summary>  /// 执行过滤和分页  /// </summary>  private IQueryable<TEntity> Execute( IQueryable<TEntity> queryable ) {      queryable.CheckNull( "queryable" );      queryable = FilterBy( queryable );      GetOrderBy();      return queryable;  }  /// <summary>  /// 过滤  /// </summary>  private IQueryable<TEntity> FilterBy( IQueryable<TEntity> queryable ) {      if ( Criteria == null )   return queryable;      return queryable.Where( Criteria.GetPredicate() );  }  #endregion  #region GetPagerList(获取分页列表)  /// <summary>  /// 获取分页列表  /// </summary>  /// <param name="queryable">数据源</param>  public PagerList<TEntity> GetPagerList( IQueryable<TEntity> queryable ) {      return Execute( queryable ).PagerResult( this );  }  #endregion     } } 

应用层服务可以这样查询。

  public PagerList<ApplicationDto> Query( ApplicationQuery query ) {    return new Query<Application>(query)     .Filter( t => t.Code == query.Code )     .Filter( t => t.Name.Contains( query.Name ) )     .Filter( t => t.Enabled == query.Enabled )     .FilterDate( t => t.CreateTime, query.BeginCreateTime, query.EndCreateTime )     .GetPagerList( Repository.Find() ).Convert( t => t.ToDto() );   } 

或

  public PagerList<ApplicationDto> Query2( ApplicationQuery query ) {    var queryObject = new Query<Application>( query )     .Filter( t => t.Code == query.Code )     .Filter( t => t.Name.Contains( query.Name ) )     .Filter( t => t.Enabled == query.Enabled )     .FilterDate( t => t.CreateTime, query.BeginCreateTime, query.EndCreateTime );    return Repository.PagerQuery( queryObject ).Convert( t => t.ToDto() );   } 

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