Linq In 子句 &谓词构建
我有两张桌子。 报告和报告数据。 ReportData 有一个约束 ReportID。
如何编写 linq 查询以返回满足 ReportData 谓词条件的所有 Report 对象? SQL 中是这样的:
SELECT * FROM Report as r
Where r.ServiceID = 3 and r.ReportID IN (Select ReportID FROM ReportData WHERE JobID LIKE 'Something%')
这就是我构建谓词的方式:
Expression<Func<ReportData, bool>> predicate = PredicateBuilder.True<ReportData>();
predicate = predicate.And(x => x.JobID.StartsWith(QueryConfig.Instance.DataStreamName));
var q = engine.GetReports(predicate, reportsDataContext);
reports = q.ToList();
这是我目前的查询构造:
public override IQueryable<Report> GetReports(Expression<Func<ReportData, bool>> predicate, LLReportsDataContext reportDC)
{
if (reportDC == null) throw new ArgumentNullException("reportDC");
var q = reportDC.ReportDatas.Where(predicate).Where(r => r.ServiceID.Equals(1)).Select(r => r.Report);
return q;
}
我也尝试执行以下操作: 公共覆盖 IQueryable GetReports(Expression> predicate, LLReportsDataContext reportDC) { if (reportDC == null) 抛出 new ArgumentNullException("reportDC");
var q = from r in reportDC.Reports
where r.ServiceID.Equals(1)
where r.ReportDatas.Where(predicate.Compile()).Select(x => r.ReportID).Contains(r.ReportID)
select r;
return q;
}
但是,我收到此异常:“查询运算符‘Where’使用的重载不受支持。”
更新 这修复了它:
var q = reportDC.Reports.AsExpandable().
Where(r => r.ReportDatas.Any(predicate.Compile()))
.Where(r => r.ServiceID.Equals(1));
I have two tables. Report and ReportData.
ReportData has a constraint ReportID.
How can I write my linq query to return all Report objects where the predicate conditions are met for ReportData? Something like this in SQL:
SELECT * FROM Report as r
Where r.ServiceID = 3 and r.ReportID IN (Select ReportID FROM ReportData WHERE JobID LIKE 'Something%')
This is how I'm building my predicate:
Expression<Func<ReportData, bool>> predicate = PredicateBuilder.True<ReportData>();
predicate = predicate.And(x => x.JobID.StartsWith(QueryConfig.Instance.DataStreamName));
var q = engine.GetReports(predicate, reportsDataContext);
reports = q.ToList();
This is my query construction at the moment:
public override IQueryable<Report> GetReports(Expression<Func<ReportData, bool>> predicate, LLReportsDataContext reportDC)
{
if (reportDC == null) throw new ArgumentNullException("reportDC");
var q = reportDC.ReportDatas.Where(predicate).Where(r => r.ServiceID.Equals(1)).Select(r => r.Report);
return q;
}
I've tried doing the following as well:
public override IQueryable GetReports(Expression> predicate, LLReportsDataContext reportDC)
{
if (reportDC == null) throw new ArgumentNullException("reportDC");
var q = from r in reportDC.Reports
where r.ServiceID.Equals(1)
where r.ReportDatas.Where(predicate.Compile()).Select(x => r.ReportID).Contains(r.ReportID)
select r;
return q;
}
However, I get the this Exception: "Unsupported overload used for query operator 'Where'."
UPDATE
This fixed it:
var q = reportDC.Reports.AsExpandable().
Where(r => r.ReportDatas.Any(predicate.Compile()))
.Where(r => r.ServiceID.Equals(1));
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关于LinqKit的
在使用LinqKit时,有时需要在实体集合中调用
AsExpandable()
并编译谓词表达式。请参阅此示例:): 如何-使用-predicate-builder-with-linq2sql-and-or-operatorQuery
AboutLinqKit
When using LinqKit, sometimes you need to call
AsExpandable()
in the entity collection and to compile the predicate expression. see this example : ): how-to-use-predicate-builder-with-linq2sql-and-or-operator