这个linq查询效率高吗？
这个linq查询效率高吗？
var qry = ((from member in this.ObjectContext.TreeMembers.Where(m => m.UserId == userId && m.Birthdate == null)
select member.TreeMemberId).Except(from item in this.ObjectContext.FamilyEvents select item.TreeMemberId));
var mainQry = from mainMember in this.ObjectContext.TreeMembers
where qry.Contains(mainMember.TreeMemberId)
select mainMember;
这会被转换为多个 sql 调用还是仅一个？可以优化吗？基本上我有 2 个表，我想从 table1 中选择那些日期时间为空的记录，并且该记录不应存在于 table2 中。
Is this linq query efficient?
var qry = ((from member in this.ObjectContext.TreeMembers.Where(m => m.UserId == userId && m.Birthdate == null)
select member.TreeMemberId).Except(from item in this.ObjectContext.FamilyEvents select item.TreeMemberId));
var mainQry = from mainMember in this.ObjectContext.TreeMembers
where qry.Contains(mainMember.TreeMemberId)
select mainMember;
Will this be translated into multiple sql calls or just one? Can it be optimised? Basically I have 2 tables, I want to select those records from table1 where datetime is null and that record should not exist in table2.
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确定查询是否会进行多次调用的最简单方法是设置数据上下文的
.Log属性。我通常将其设置为写入DebugOutputWriter。可以找到此类类的一个很好的示例 此处。然而，对于一般的思考方式来说，如果您使用的类的属性不直接映射到 where 子句或 join 子句中的数据库字段，那么它通常会进行多次调用。从您提供的内容来看，您的情况似乎并非，但我不能绝对确定并建议使用上面列出的方法。
The easiest way to find out if the query will make multiple calls is to set the
.Logproperty of the data context. I typically set it to write to aDebugOutputWriter. A good example for this kind of class can be found here.For a general way of thinking about it however, if you use a property of your class that does not directly map to a database field in a where clause or a join clause, it will typically make multiple calls. From what you have provided, it looks like this is not the case for your scenario, but I can't absolutely certain and suggest using the method listed above.