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Repository 简化实现多条件查询

Repository 在做查询的时候,如果查询条件多的话,linq查询表达式会写的很复杂,比如:

 1 public IQueryable<Student> Get(int id, string name, string address, Status? status, DateTime createTime)  2 {  3     var query = _entities;  4     if(id != 0)  5     {  6         query = query.where(x => x.Id == id);  7     }  8     if(!string.IsNullOrWhiteSpace(name))  9     { 10         query = query.where(x => x.Name.Contains(name)); 11     } 12     if(!string.IsNullOrWhiteSpace(address)) 13     { 14         query = query.where(x => x.Address.Contains(address)); 15     } 16     if(status.HasValue) 17     { 18         query = query.where(x => x.Status == status.Value); 19     } 20     if(createTime != null) 21     { 22         query = query.where(x => x.CreateTime == createTime); 23     } 24     // ... 25  26     return query; 27 }

可以看到,查询条件多的话,我们会写很多的if判断,代码看起来很不美观,解决方式使用Expression<Func<T, bool>>,示例代码:

using System.Linq.Expressions;  public IQueryable<Student> Get(int id, string name, string address, Status? status, DateTime createTime) {     Expression<Func<Student, bool>> studentFunc = x =>             (id == 0 || x.Id == id) &&             (string.IsNullOrWhiteSpace(name) || x.Name.Contains(name)) &&             (string.IsNullOrWhiteSpace(address) || x.Address.Contains(address)) &&             (!status.HasValue || x.Status == status.Value) &&             (createTime == null || x.CreateTime <= createTime);      return _entities.Where(studentFunc);

生成示例sql代码:

1 SELECT `x`.`id`, `x`.`name`, `x`.`address`, `x`.`status`, `x`.`create_time` 2 FROM `students` AS `x` 3 WHERE (`x`.`id` = 2) 4 AND (`x`.`status` = 0) AND (`x`.`create_time` == '2017-04-25T16:24:29.769+08:00')) 

原文来源:https://www.cnblogs.com/xishuai/p/repository-query-linq-expression.html

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未经允许不得转载:张拓的天空 » Repository 简化实现多条件查询
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