ABP学习实践(四)--分页查询

前面两篇文章只写了增删改功能，并不是把查询功能遗漏了，本篇就单独来讨论分页查询。分页查询很常用，实现并不难，但是想要用起来方便舒服还是要花些心思。虽然分页查询的实现跟ABP框架并没有什么关系，但是为了延续性暂且还是放在这里了。

对于分页查询来讲，需要注意的有两点：一是查询条件的处理，用户的输入是多样化的、无法预知的，查询规则要足够灵活和简单；二是查询结果的分页处理，一般是根据当前页码和每页记录数来展示数据，要有足够快的查询效率和响应速度。

1.定义查询条件输入类

在应用层AbpDemo.Application新建用于查询输入的基类，包含过滤条件和排序规则两个属性。

    public class PagedBaseDto{/// <summary>/// 过滤条件/// </summary>public List<DataFilter> Filters { get; set; }/// <summary>/// 排序规则/// </summary>public List<DataSort> Sorts { get; set; }}

其中过滤条件为：

    public class DataFilter{public string FilterName { get; set; }public string FilterValue { get; set; }public FilterType FilterType { get; set; }public ExpressionType ExpressionType { get; set; }}public enum FilterType{String,Int,Long,Boolean}public enum ExpressionType{/// <summary>///  like/// </summary>Contains,/// <summary>/// 等于/// </summary>Equal,/// <summary>/// 小于/// </summary>LessThan,/// <summary>/// 小于等于/// </summary>LessThanOrEqual,/// <summary>/// 大于/// </summary>GreaterThan,/// <summary>/// 大于等于/// </summary>GreaterThanOrEqual}

排序方式为：

    public class DataSort{public string SortName { get; set; }public SortType SortType { get; set; }}public enum SortType{/// <summary>/// 升序/// </summary>Asc,/// <summary>/// 降序/// </summary>Desc}

2.处理查询条件并返回结果

在应用层的基类AbpDemoAppServiceBase中创建一个方法用于处理查询条件并返回结果。方法的输入参数继承了上一步的基类PagedBaseDto。

        /// <summary>/// 分页查询/// </summary>/// <param name="input"></param>/// <returns></returns>public virtual async Task<IQueryable<TEntity>> Page(TPagedInput input){IQueryable<TEntity> query = Repository.GetAll();var sourceExpression = query.Expression;//where表达式if (input.Filters != null){foreach (var filter in input.Filters){if (string.IsNullOrWhiteSpace(filter.FilterName) || string.IsNullOrWhiteSpace(filter.FilterValue)){continue;}var whereLambdaExtenstion = GetLambdaExtention(filter);sourceExpression = Expression.Call(typeof(Queryable), "Where", new Type[1] { typeof(TEntity) }, sourceExpression, Expression.Quote(whereLambdaExtenstion.GetLambda()));}}if (input.Sorts != null){ParameterExpression parameter = Expression.Parameter(typeof(TEntity), "x");string methodAsc = "OrderBy";string methodDesc = "OrderByDescending";foreach (var sort in input.Sorts){if (string.IsNullOrWhiteSpace(sort.SortName)){continue;}MemberExpression body = Expression.PropertyOrField(parameter, sort.SortName);sourceExpression = Expression.Call(typeof(Queryable), sort.SortType == SortType.Asc ? methodAsc : methodDesc, new Type[] { typeof(TEntity), body.Type }, sourceExpression, Expression.Quote(Expression.Lambda(body, parameter)));methodAsc = "ThenBy";methodDesc = "ThenByDescending";}}query = query.Provider.Execute<IEnumerable<TEntity>>(sourceExpression).AsQueryable();//result.TotalCount = query.Count();//if (input.PageSize != -1)//{//    result.Items = query.Skip((input.PageIndex - 1) * input.PageSize).Take(input.PageSize).MapTo<IEnumerable<TEntityDto>>().ToList();//}//else//{//    result.Items = query.MapTo<IEnumerable<TEntityDto>>().ToList();//}return await Task.FromResult(query);}//Lambda表达式处理private LambdaExtention<TEntity> GetLambdaExtention(DataFilter filter){var whereLambdaExtenstion = new LambdaExtention<TEntity>();switch (filter.FilterType){case FilterType.Int:whereLambdaExtenstion.GetExpression(filter.FilterName, int.Parse(filter.FilterValue), filter.ExpressionType);break;case FilterType.Long:whereLambdaExtenstion.GetExpression(filter.FilterName, long.Parse(filter.FilterValue), filter.ExpressionType);break;case FilterType.Boolean:whereLambdaExtenstion.GetExpression(filter.FilterName, filter.FilterValue.ToUpper() == "TRUE" ? true : false, filter.ExpressionType);break;default:whereLambdaExtenstion.GetExpression(filter.FilterName, filter.FilterValue, filter.ExpressionType);break;}return whereLambdaExtenstion;}

由于ABP框架中使用的是仓储模式，仓储模式一般使用Lambda表达式或Linq语句来进行查询，因此需要将输入的查询条件转化成Lambda表达式。这个过程就需要用到Lambda表达式相关的辅助类。

    /// <summary>/// 动态Lambda构造类/// </summary>/// <typeparam name="Dto"></typeparam>public class LambdaExtention<Dto> where Dto : class{private List<Expression> m_lstExpression = null;private ParameterExpression m_Parameter = null;public LambdaExtention(){m_lstExpression = new List<Expression>();m_Parameter = Expression.Parameter(typeof(Dto), "x");}//构造表达式，存放到m_lstExpression集合里面public void GetExpression(string strPropertyName, object strValue, ExpressionType expressType){Expression expRes = null;MemberExpression member = Expression.PropertyOrField(m_Parameter, strPropertyName);if (member.Type == typeof(int?) || member.Type == typeof(int)){strValue = Convert.ToInt32(strValue);}else if (member.Type == typeof(DateTime?) || member.Type == typeof(DateTime)){strValue = Convert.ToDateTime(strValue);}if (expressType == ExpressionType.Contains){expRes = Expression.Equal(member, Expression.Constant(strValue, member.Type));}else if (expressType == ExpressionType.Equal){expRes = Expression.Equal(member, Expression.Constant(strValue, member.Type));}else if (expressType == ExpressionType.LessThan){expRes = Expression.LessThan(member, Expression.Constant(strValue, member.Type));}else if (expressType == ExpressionType.LessThanOrEqual){expRes = Expression.LessThanOrEqual(member, Expression.Constant(strValue, member.Type));}else if (expressType == ExpressionType.GreaterThan){expRes = Expression.GreaterThan(member, Expression.Constant(strValue, member.Type));}else if (expressType == ExpressionType.GreaterThanOrEqual){expRes = Expression.GreaterThanOrEqual(member, Expression.Constant(strValue, member.Type));}//return expRes;m_lstExpression.Add(expRes);}//得到Lamada表达式的Expression对象public Expression<Func<Dto, bool>> GetLambda(){Expression whereExpr = null;foreach (var expr in m_lstExpression){if (whereExpr == null) whereExpr = expr;else whereExpr = Expression.And(whereExpr, expr);}if (whereExpr == null)return null;return Expression.Lambda<Func<Dto, bool>>(whereExpr, m_Parameter);}}

3.对查询结果进行分页操作

在原有分页查询输入基类PagedBaseDto的基础上添加当前页码和每页记录数的属性。

    public class PagedBaseDto{/// <summary>/// 过滤条件/// </summary>public List<DataFilter> Filters { get; set; }/// <summary>/// 排序规则/// </summary>public List<DataSort> Sorts { get; set; }private int pageSize = 10;/// <summary>/// 每页记录数/// </summary>public int PageSize{get { return pageSize; }set { pageSize = value; }}private int pageIndex = 1;/// <summary>/// 当前页码/// </summary>public int PageIndex{get { return pageIndex; }set { pageIndex = value; }}}

而应用服务基类AbpDemoAppServiceBase中的分页查询方法就可以改为：

        /// <summary>/// 分页查询/// </summary>/// <param name="input"></param>/// <returns></returns>public virtual async Task<PagedResultDto<TEntityDto>> Page(TPagedInput input){if (input == null){return new PagedResultDto<TEntityDto>();}PagedResultDto<TEntityDto> result = new PagedResultDto<TEntityDto>();IQueryable<TEntity> query = Repository.GetAll();var sourceExpression = query.Expression;//where表达式if (input.Filters != null){foreach (var filter in input.Filters){if (string.IsNullOrWhiteSpace(filter.FilterName) || string.IsNullOrWhiteSpace(filter.FilterValue)){continue;}var whereLambdaExtenstion = GetLambdaExtention(filter);sourceExpression = Expression.Call(typeof(Queryable), "Where", new Type[1] { typeof(TEntity) }, sourceExpression, Expression.Quote(whereLambdaExtenstion.GetLambda()));}}if (input.Sorts != null){ParameterExpression parameter = Expression.Parameter(typeof(TEntity), "x");string methodAsc = "OrderBy";string methodDesc = "OrderByDescending";foreach (var sort in input.Sorts){if (string.IsNullOrWhiteSpace(sort.SortName)){continue;}MemberExpression body = Expression.PropertyOrField(parameter, sort.SortName);sourceExpression = Expression.Call(typeof(Queryable), sort.SortType == SortType.Asc ? methodAsc : methodDesc, new Type[] { typeof(TEntity), body.Type }, sourceExpression, Expression.Quote(Expression.Lambda(body, parameter)));methodAsc = "ThenBy";methodDesc = "ThenByDescending";}}query = query.Provider.Execute<IEnumerable<TEntity>>(sourceExpression).AsQueryable();result.TotalCount = query.Count();if (input.PageSize != -1){result.Items = query.Skip((input.PageIndex - 1) * input.PageSize).Take(input.PageSize).MapTo<IEnumerable<TEntityDto>>().ToList();}else{result.Items = query.MapTo<IEnumerable<TEntityDto>>().ToList();}return await Task.FromResult(result);}

其中PagedResultDto是ABP框架自带的分页查询结果的数据结构，这里没有改动直接用了。

4.在派生类中使用分页方法

由于分页查询的方法是在基类中定义的，继承基类的派生类可以直接使用，只需要根据基类的约束条件修改下代码就行了。

应用服务接口：

    /// <summary>/// 货品管理-应用服务接口/// </summary>public interface IGoodsAppService: IAbpDemoAppServiceBase<Goods,DetailGoodsDto,string,CreateGoodsDto,UpdateGoodsDto, PagedGoodsDto>,IApplicationService{}

应用服务：

    /// <summary>/// 货品管理-应用服务/// </summary>public class GoodsAppService: AbpDemoAppServiceBase<Goods,DetailGoodsDto,string,CreateGoodsDto,UpdateGoodsDto,PagedGoodsDto>,IGoodsAppService{public GoodsAppService(IRepository<Goods,string> repository):base(repository){}}

其中新加的类PagedGoodsDto是继承于第一步创建的PagedBaseDto类。

源代码示例-Github