[英]Use Include() method in repository
我在EF 5中有以下內容:
var a = context.Posts.Include(x => x.Pack).Select(x => x.Pack.Id).ToList();
這有效。 然后我嘗試在我的通用存儲庫中復制它:
public IQueryable<T> Include<T>(Expression<Func<T, Boolean>> criteria) where T : class
{
return _context.Set<T>().Include(criteria);
}
但在這種情況下,我無法執行以下操作:
var b = repository.Include<Post>(x => x.Pack).Select(x => x.Pack.Id).ToList();
我收到錯誤:
無法將類型'Data.Entities.Pack'隱式轉換為'bool'
我怎么解決這個問題?
我應該在Include()方法中更改什么?
嘗試:
更改
Expression<Func<T, Boolean>> criteria
至
Expression<Func<T, object>> criteria
編輯:要包含多個實體,您需要添加“包含”擴展名:
public static class IncludeExtension
{
public static IQueryable<TEntity> Include<TEntity>(this IDbSet<TEntity> dbSet,
params Expression<Func<TEntity, object>>[] includes)
where TEntity : class
{
IQueryable<TEntity> query = null;
foreach (var include in includes)
{
query = dbSet.Include(include);
}
return query == null ? dbSet : query;
}
}
然后你可以像這樣使用它:
repository.Include(x => x.Pack, x => x.Pack.Roles, ...).Select(x => x.Pack.Id).ToList();
只需確保“repository”返回“DbSet”對象。
我使用了接受的答案,但不得不為EntityFramework Core稍微修改一下。 根據我的經驗,我必須保持鏈條運行或以前的查詢引用被覆蓋。
public IQueryable<TEntity> Include(params Expression<Func<TEntity, object>>[] includes)
{
IIncludableQueryable<TEntity, object> query = null;
if(includes.Length > 0)
{
query = _dbSet.Include(includes[0]);
}
for (int queryIndex = 1; queryIndex < includes.Length; ++queryIndex)
{
query = query.Include(includes[queryIndex]);
}
return query == null ? _dbSet : (IQueryable<TEntity>)query;
}
這就是我們在EF 6中所做的結果
public IEnumerable<T> GetIncludes(params Expression<Func<T, Object>>[] includes)
{
IQueryable<T> query = table.Include(includes[0]);
foreach (var include in includes.Skip(1))
{
query = query.Include(include);
}
return query.ToList();
}
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