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。
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, LevelFROM 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);
}
}
}
