我有这个方法:
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(是否缺少强制转换?)
有谁知道如何使包含列表动态化?
谢谢
最佳答案
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于魔法字符串。
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();
}
}
要使这些动态化,您可以这样做:
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);
}
}
它是这样使用的:
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
);
关于c# - 在查询中预先加载的动态包含语句 - EF 4.3.1,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/10001061/