我有此方法:
public CampaignCreative GetCampaignCreativeById(int id)
{
using (var db = GetContext())
{
return db.CampaignCreatives
.Include("Placement")
.Include("CreativeType")
.Include("Campaign")
.Include("Campaign.Handshake")
.Include("Campaign.Handshake.Agency")
.Include("Campaign.Product")
.AsNoTracking()
.Where(x => x.Id.Equals(id)).FirstOrDefault();
}
}
我想使包含列表动态化。我尝试过:
public CampaignCreative GetCampaignCreativeById(int id, string[] includes)
{
using (var db = GetContext())
{
var query = db.CampaignCreatives;
foreach (string include in includes)
{
query = query.Include(include);
}
return query.AsNoTracking()
.Where(x => x.Id.Equals(id)).FirstOrDefault();
}
}
但是它没有编译。我收到此错误:
无法将类型'System.Data.Entity.Infrastructure.DbQuery'隐式转换为'System.Data.Entity.DbSet'。存在显式转换(您是否缺少演员表?)
有人知道如何使包含列表动态化吗?
谢谢
使query
变量可查询:
public CampaignCreative GetCampaignCreativeById(int id, string[] includes)
{
using (var db = GetContext())
{
var query = db.CampaignCreatives.AsQueryable();
foreach (string include in includes)
{
query = query.Include(include);
}
return query
.AsNoTracking()
.Where(x => x.Id.Equals(id))
.FirstOrDefault();
}
}
我更喜欢定义包含的非字符串表达方式。主要是因为它不依赖魔术字符串。
对于示例代码,它看起来像这样:
public CampaignCreative GetCampaignCreativeById(int id) {
using (var db = GetContext()) {
return db.CampaignCreatives
.Include(cc => cc.Placement)
.Include(cc => cc.CreativeType)
.Include(cc => cc.Campaign.Select(c =>
c.Handshake.Select(h => h.Agency)))
.Include(cc => cc.Campaign.Select(c => c.Product)
.AsNoTracking()
.Where(x => x.Id.Equals(id))
.FirstOrDefault();
}
}
并使这些动态,这是您的方法:
public CampaignCreative GetCampaignCreativeById(
int id,
params Expression<Func<T, object>>[] includes
) {
using (var db = GetContext()) {
var query = db.CampaignCreatives;
return includes
.Aggregate(
query.AsQueryable(),
(current, include) => current.Include(include)
)
.FirstOrDefault(e => e.Id == id);
}
}
这样使用:
var c = dataService.GetCampaignCreativeById(
1,
cc => cc.Placement,
cc => cc.CreativeType,
cc => cc.Campaign.Select(c => c.Handshake.Select(h => h.Agency)),
cc => cc.Campaign.Select(c => c.Product
);
通过使用IQueryable<CampaignCreative>
而不是var
向编译器提供提示也将起作用。
IQueryable<CampaignCreative> query = db.CampaignCreatives;
// or
DbQuery<CampaignCreative> query = db.CampaignCreatives;
[使用var
时,编译器会为DbSet<T>
推断query
,它比实现Include
的DbQuery<T>
(即DbSet<T>
(= IQueryable<T>
的基类))返回的类型更具体,因此您无法再将结果分配给query
变量。因此,query = query.Include(include)
行上的编译器错误。
我编写了此方法,以根据实体的类型动态地检索任何实体集。我使用IDbEntity
接口提供了一个有效的密钥来搜索所有类中的userId。Util.GetInverseProperties<T>()
方法用于获取Include
语句中所需的属性。
public IEnumerable<T> GetItems<T>(string userId) where T : class, IDbEntity
{
var query = db.Set<T>().Where(l => l.UserId==userId);
var props = Util.GetInverseProperties<T>();
foreach (var include in props)
query = query.Include(include.Name);
return query
.AsNoTracking()
.ToList();
}
public interface IDbEntity
{
public string UserId { get; set; }
}
public static List<PropertyInfo> GetInverseProperties<T>()
{
return typeof(T)
.GetProperties()
.Where(p => Attribute.IsDefined(p, typeof(InversePropertyAttribute)))
.ToList();
}