Linq语句具有两个select和where条件

Question

I have this linq to SQL where I just want to return one Disease with the connecting drug. But what this is doing is returning all Diseases and only populating the drug that meets the where condition.

Do I need to select the drugs and then the Disease for this to work?

    public List<Model.Disease> GetDiseaseById(Guid DiseaseId)
    {
       var Disease = (from Diseases in db.Diseases
                        join dr in db.DrugDiseases on  equals d.DrugId on dr.DrugId 
                        join rdDiseases on rdDiseases.Diseases equals rd.DiseaseId on dr.DiseaseId
                      where (aDrug.DiseaseId == DiseaseId)
                      select new Model.Disease 
                    {
                       DiseaseId = rdDiseases.DiseaseId,
                       DiseaseName = rdDiseases.DiseaseName,
                       drug = (from d in db.Drug
                                join dr1 in db.DrugDiseases on  equals d.DrugId on dr1.DrugId 
                                join rd1Diseases on rdDiseases.Diseases equals rd.DiseaseId on dr1.DiseaseId
                               where (Diseases.DiseaseId == d.DiseaseId && d.DiseaseId == DiseaseId)
                               select new drug
                            {
                              DrugId = d.drug,
                              DrugName = d.drugName}).OrderBy(m => m.DrugName).ToList(),
                   }).OrderBy(d => d.DiseaseName).ToList().FirstOrDefault();
       return Disease;                       
     }

Answer 1

Based on the comments above, you just need one join and this should be straightforward. You should read about Joins in LINQ and LINQ in general. Also, since you are looking for just one disease, why are you returning a list? The code below should work:

public Model.Disease GetDiseaseById(Guid DiseaseId)
{
   return (from Disease in db.Diseases
               where Disease.DiseaseId == DiseaseId
               orderby Disease.DiseaseName
               join d in db.Drug on Disease.DiseaseId equals d.DiseasesId
               select new Model.Disease
               {
                   DiseaseId = Disease.DiseaseId
                   DiseaseName = Disease.DiseaseName
                   drug = new { DrugId = d.DrugId, DrugName = d.DrugName }
               }).FirstOrDefault();
}