动态包含在查询中急切加载的语句 - EF 4.3.1

Question

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();
            }
        }

我想列出包含动态的列表.我试过了:

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.我收到了这个错误:

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(您是否错过了演员？)

有谁知道如何制作包含动态的列表？

谢谢

Answer 1

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弦.

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();
    }
}

为了使这些动态,这就是你如何做到这一点:

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);
    }
}

使用方式如下:

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
);

Answer 2

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();                    
    }
}