How can I select data from multiple tables? - linq

Question

In my MVC project, I have some tables like this:
Form (FormID, SectionID)
Section (SectionID, SectionName)
SectionQuestion (SectionID, QuestionID)
Question (QuestionID, Content)
A form has multiple sections, and a section has some questions.
I can get all question for the FormID. But I want to get a list of sections (which contain questions) for the model.
It means in the view I want to do something like this:
#Model IEnumerable<MedialForm.Models.Sections>
foreach (var section in Model)
{
//Show questions
}
Can you guys help me? :)

Answer 1

You will not see a list of sections for a form, since the Form can only have 1 section. (i.e. the SectionID is defined in Form, and not FormID in Section). However the following Linq query will return the section and the associated questions for a specified FormID:
void Main()
{
var sections =
new []
{
new Section { SectionID = 1, SectionName = "SectionName1" },
new Section { SectionID = 2, SectionName = "SectionName2" }
};
var forms =
new []
{
new Form { FormID = 1, SectionID = 1 },
new Form { FormID = 2, SectionID = 1 },
new Form { FormID = 3, SectionID = 2 },
new Form { FormID = 4, SectionID = 2 }
};
var questions =
new[]
{
new Question { QuestionID = 1, Content = "Question1" },
new Question { QuestionID = 2, Content = "Question2" }
};
var sectionQuestions =
new[]
{
new SectionQuestion { SectionID = 1, QuestionID = 1 },
new SectionQuestion { SectionID = 2, QuestionID = 1 },
new SectionQuestion { SectionID = 2, QuestionID = 2 }
};
var formId = 4;
var result = forms
.Join(
sections,
f => f.SectionID,
s => s.SectionID,
(f, s) => new { Form = f, Section = s })
.Join(
sectionQuestions,
jfs => jfs.Section.SectionID,
sq => sq.SectionID,
(jfs, sq) => new { Form = jfs.Form, Section = jfs.Section, sq.QuestionID })
.Join(
questions,
jfsq => jfsq.QuestionID,
q => q.QuestionID,
(jfsq, q) => new { Form = jfsq.Form, Section = jfsq.Section, Question = q })
.Where(f => f.Form.FormID == formId)
.GroupBy(f => f.Section.SectionID)
.Select(grp => new { SectionID = grp.Key, Questions = grp.Select(g => g.Question)});
Console.WriteLine($"For Form: {formId} the following sections with their questions were found: {String.Join(", ", result.Select(r => $"SectionID: {r.SectionID}, QuestionIDs: [{String.Join(", ", r.Questions.Select(q => q.QuestionID))}]"))}");
}
public class Form
{
public Int32 FormID { get; set; }
public Int32 SectionID { get; set; }
}
public class Section
{
public Int32 SectionID { get; set; }
public String SectionName { get; set; }
}
public class SectionQuestion
{
public Int32 SectionID { get; set; }
public Int32 QuestionID { get; set; }
}
public class Question
{
public Int32 QuestionID { get; set; }
public String Content { get; set; }
}
This will return the following result:
For Form: 4 the following sections with their questions were found: SectionID: 2, QuestionIDs: [1, 2]