SQL Server 2005开始,我们可以直接通过CTE来支持递归查询,CTE即公用表表达式
公用表表达式(CTE),是一个在查询中定义的临时命名结果集将在from子句中使用它。每个CTE仅被定义一次(但在其作用域内可以被引用任意次),并且在该查询生存期间将一直生存。可以使用CTE来执行递归操作。
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DECLARE @ Level INT =3 ; WITH cte_parent(CategoryID,CategoryName,ParentCategoryID, Level ) AS ( SELECT category_id,category_name,parent_category_id,1 AS Level FROM TianShenLogistic.dbo.ProductCategory WITH (NOLOCK) WHERE category_id IN ( SELECT category_id FROM TianShenLogistic.dbo.ProductCategory WHERE parent_category_id=0 ) UNION ALL SELECT b.category_id,b.category_name,b.parent_category_id,a. Level +1 AS Level FROM TianShenLogistic.dbo.ProductCategory b INNER JOIN cte_parent a ON a.CategoryID = b.parent_category_id ) SELECT CategoryID AS value, CategoryName as label, ParentCategoryID As parentId, Level FROM cte_parent WHERE Level <=@ Level ; public static List<LogisticsCategoryTreeEntity> GetLogisticsCategoryByParent( int ? level ) { if ( level < 1) return null ; var dataResult = CategoryDA.GetLogisticsCategoryByParent( level ); var firstlevel = dataResult. Where (d => d. level == 1).ToList(); BuildCategory(dataResult, firstlevel); return firstlevel; } private static void BuildCategory(List<LogisticsCategoryTreeEntity> allCategoryList, List<LogisticsCategoryTreeEntity> categoryList) { foreach (var category in categoryList) { var subCategoryList = allCategoryList. Where (c => c.parentId == category.value).ToList(); if (subCategoryList. Count > 0) { if (category.children == null ) category.children = new List<LogisticsCategoryTreeEntity>(); category.children.AddRange(subCategoryList); BuildCategory(allCategoryList, category.children); } } } |
原文链接:http://leelei.blog.51cto.com/856755/1957792