Linq在子句和谓词中的构建

Question

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));

Answer 1

Query

ReportDatas
.Where( reportData => reportData.StartsWith( "Something%" ) &&
     reportData.Report.Id ==3)
.Select( reportData => reportData.Report )
.Distinct()

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