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EntityFramework Codefirst Select 查询指定列
本笔记解决如下两个问题：
1、查询返回指定列。
2、查询指定列时报错如下：
The entity or complex type ‘DataBase.AccordionModels‘ cannot be constructed in a LINQ to Entities query.
一、环境中类定义如下：
DataBaseContext,
public DataBaseContext() : base("default") { public DbSet<UserModels> UserContext { get; set; } public DbSet<PigModels> PigContext { get; set; } public DbSet<AccordionModels> AccordionContext { get; set; } public DbSet<HrefModels> HrefContext { get; set; } }
AccordionModels:
public class AccordionModels { [Required] [Key] public string ID { get; set; } [Required] [Display(Name = "名称")] public string title { get; set; } [Display(Name = "icon")] public string icon { get; set; } [Display(Name = "顺序号")] public int order { get; set; } public virtual ICollection<HrefModels> Hrefs { get; set; } }
HrefModels:
public class HrefModels { [Required] [Key] public string ID { get; set; } [Required] [Display(Name = "图标")] public string icon { get; set; } [Display(Name = "链接")] public string link { get; set; } [Display(Name = "名称")] public string title { get; set; } public int iFrame { get; set; } public virtual AccordionModels Accordion { get; set; } }
二、查询方法
（1）报错的查询方法：当采用如下写法查询时，会抛出异常 Message:The entity or complex type ‘DataBase.AccordionModels‘ cannot be constructed in a LINQ to Entities query.
List<AccordionModels> accordions = new List<AccordionModels>(); accordions = context.AccordionContext.Select(a => new AccordionModels() { ID = a.ID, title = a.title, icon = a.icon }).ToList();
可用如下两种方法：注意Select中的内容：1、新建一个实体类 AccordionView
List<AccordionView> accordions = new List<AccordionView>(); accordions = context.AccordionContext.Select(a => new AccordionView() { ID = a.ID, title = a.title, icon = a.icon }).ToList();
2、查询之后在转换
List<AccordionModels> AccordionModels = context.AccordionContext.Select(a => new { a.ID, a.title, a.icon }).ToList() .Select(b => new AccordionModels() { ID = b.icon, title = b.title, icon = b.icon }).ToList();
EntityFramework Codefirst Select 查询指定列
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