Ron 2.0

在使用linq to entities 撈資料的時候, 出現了這樣的錯誤訊息:

The entity or complex type 'BlogMgmtModel.BlogArticle' cannot be constructed in a LINQ to Entities query.

 

出錯的程式碼如下:

BlogArticle q1 = _blogArticleRepository.Query().Where(r => r.BlogArticleID > 10)
    .Select(rlt => new BlogArticle { AuditStatus = rlt.AuditStatus, BlogArticleID = rlt.BlogArticleID })
    .FirstOrDefault();

 

上Stackoverflow查了一下, 有下面這一段說明

In Linq-to-Entities you can only project to an anonymous type or a regular class. You can't project to an existing entity type. You can with linq-to-objects like so..

因此, 我們這邊必須將程式改成

//solusion A
var blogArticle = _blogArticleRepository.Query().Where(r => r.BlogArticleID > 10)
    .Select(rlt => new { AuditStatus = rlt.AuditStatus, BlogArticleID = rlt.BlogArticleID })
    .FirstOrDefault();

//solusion B
BlogArticle blogArticle2 = _blogArticleRepository.Query().Where(r => r.BlogArticleID > 10)
    .AsEnumerable()
    .Select(rlt => new BlogArticle { AuditStatus = rlt.AuditStatus, BlogArticleID = rlt.BlogArticleID })
    .FirstOrDefault();