如何在 lambda 中进行左连接

Question

    var item= (from t1 in _dbEntities.PurchaseSales
                join t2 in _dbEntities.ItemTypes on t1.ItemTypeID equals t2.ID
                where t2.ID.Equals(null)
               select t2).ToList();

左加入怎么办

Answer 1

使用DefaultIfEmpty:

var item= (from t1 in _dbEntities.PurchaseSales
                join t2 in _dbEntities.ItemTypes on t1.ItemTypeID equals t2.ID into t
                from l in t.DefaultIfEmpty()
                where l == null
               select t1).ToList();