LINQ关联-实体框架

Question

I have three tables and I have used edmx designer to add associations between them. Below is how they are linked.

(table1) Loans - (table 2) Investor : Many to One relationship (Table2) Investor - (Table3) InvestorInfo : One to Many relationship

I want to get [1] Total loans count sold to one investor, [2] Investor name and [3] investor's service fee which is stored in Table3 at idx = 2005 for each investor ("investor id & idx" is primary key of table3 - InvestorInfo table).

How do I do that in below query? I am forced to select 'FirstOrDefault()' to access any column in Table3 (See commented lines). If I use FirstOrDefualt, I get a record where idx = 1 and not 2005.

 var loanPurchaseData = (from cd in entity.Table1
                        //where cd.Table2.Table3.Select(x => x.IDX == 2005)
                        //where cd.ULDD_SET_POOLS.ULDD_SET_POOLDT.FirstOrDefault().SORT_ID == 2005
                        group cd by new { cd.Table4.PurchaseDate, cd.Number } into grp
                        select new
                        {
                            investor = grp.FirstOrDefault().Investor,
                            no_of_loans = grp.Count(),                                               
                            sort_id = grp.FirstOrDefault().Table2.Table3.FirstOrDefault().SORT_ID,
                            service_fee_rate = grp.FirstOrDefault().Table2.Table3.FirstOrDefault().DT_REAL_PERC_VALUE
                        }).ToList();

Answer 1

Your question is not very clear - I don't understand whether idx is in Table3 or Table1, and what you want to select, but I will assume you have a many-one-many schema, where an Investor has zero or more Loans & zero or more InvestorInfos . You want to get, say, all of the loans which join to investor info with idx = 2005 . Correct me if I'm wrong, and correct your question if I'm right!

Starting with your InvestorInfo object, you know that there's only one Investor but there will be zero or more Loans .

// only one InvestorInfo for idx, but this isn't clear in your question
var investorInfo = context.InvestorInfos.SingleOrDefault(i => i.idx == 2005);

var loans = investorInfo.Investor.Loans;

The crux of your problem is that you cannot get 'the loan service fee' for an investor info. Why not? Because that investor has 5 loans. Which one do you want?

-- we can get the maximum, minimum, sum, etc...
var max = loans.Max(l => l.DT_REAL_PERC_VALUE);
var min = loans.Min(l => l.DT_REAL_PERC_VALUE);
var min = loans.Sum(l => l.DT_REAL_PERC_VALUE);

Again it's not clear what you are trying to do, nor what your data actually looks like, but in a one-many relationship you will necessarily have more than one of the 'many' side for each of the 'one' side.

---

To get the max, use the Max operator.

service_fee = grp.Max(l => l.Table2.Table3.Max(t => t.DT_REAL_PERC_VALUE))