NetCore 左连接demo

表1 Entities数据集
表2 Fraentity数据集

关联字段
Entities 的 SponsorId
Fraentity 的_id

表2 实体类 FranchiseesBaseInfo

var DataEntity= Entities.GroupJoin(Fraentity, p => p.SponsorId, f => f._id.ToString(), (p, f) => f.DefaultIfEmpty(new FranchiseesBaseInfo()).Select(z=> new AdvertFranDto
       {
            _id = p._id.ToString(),
            FranchiseesName = z.FranchiseesName,
            AdvertType = p.AdvertType,
            AdvertGroup = p.AdvertGroup,
            Title = p.Title,
            ImageURL = p.ImageURL,
            TurnURL = p.TurnURL,
            IsShow = p.IsShow,
            AdvertSort = p.AdvertSort,
            Price = p.Price,
            SponsorId = p.SponsorId,
            Provice = p.Provice,
            City = p.City,
            County = p.County,
            EndTime = p.EndTime

        })).SelectMany(p=>p).ToList();