Join Multiple DataTables using LINQ

Let us say we have three DataTables Student Details, Student Marks and Subjects. And we need to see the Marks of the Students in Each Subjects, so now we need to Join these three Tables with the Primary and Foreign key of these tables.

Student Details

StudentName	StudentID (Primary Key)
AAA	111
BBB	222

Student Marks

StudentID (Foreign Key)	SubjectID (Foreign Key)	Marks
111	1	89
111	2	90
222	1	95
222	2	93

 Subjects

SubjectID (Primary Key)	SubjectName
1	Chemistry
2	Physical Science

 Expected Results

StudentID	StudetName	Subject	Marks
111	AAA	Chemistry	89
111	AAA	Physical Science	90
222	BBB	Chemistry	95
222	BBB	Physical Science	93

Let us consider all the three tables are populated with the data mentioned above and now the below code will join these three DataTables and results the expected results.

List<summary> sum = (from dataRows1 in StudentDetails.AsEnumerable()
                                 join dataRows2 in StudentMarks.AsEnumerable()
                                 on Convert.ToString(dataRows1["StudentID"]).ToUpper() equals Convert.ToString(dataRows2["StudentID"]).ToUpper() into position1
                                 from dataRows2 in position1
                                 join dataRows3 in SubjectDetails.AsEnumerable()
                                 on dataRows2["SubjectID"] equals dataRows3["SubjectID"] into position2
                                 from dataRows3 in position2.DefaultIfEmpty()
                                 select new Summary
                                 {
                                     StudentID = dataRows1 != null ? Convert.ToString(dataRows1["StudentID"]) : "",
                                     StudentName = dataRows1 != null ? Convert.ToString(dataRows1["StudentName"]) : "",
                                     Subject = dataRows3 != null ? Convert.ToString(dataRows3["SubjectName"]) : "",
                                     Mark = dataRows2 != null ? Convert.ToString(dataRows2["Marks"]) : ""
                                 }).ToList();

Output of the above code Executed in Console Application.