Using Entity Framework Core for Data Access & Relational Mapping/

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Challenge Solution: Save Data

Challenge Solution: Save Data

Review the solution to save data to a school database.

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Solution

The project below demonstrates the solution to the challenge:

using Microsoft.EntityFrameworkCore;
using SaveData.Models.Entities;

namespace SaveData.Models.Data
{
    public class SchoolContext : DbContext
    {
        public SchoolContext()
        {

        }

        public SchoolContext(DbContextOptions<SchoolContext> options) : base(options)
        {

        }

        public virtual DbSet<Instructor> Instructors { get; set; }
        public virtual DbSet<Student> Students { get; set; }
        public virtual DbSet<Department> Departments { get; set; }
        public virtual DbSet<Course> Courses { get; set; }
        public virtual DbSet<StudentCourse> StudentCourses { get; set; }

        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {

            if (!optionsBuilder.IsConfigured)
            {
                optionsBuilder.UseSqlite("data source=output/School.db");
            }
        }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            modelBuilder.Entity<Instructor>()
                        .HasOne(d => d.Department)
                        .WithMany(i => i.Instructors)
                        .HasForeignKey(inst => inst.DepartmentCode);

            modelBuilder.Entity<StudentCourse>().HasKey(sc => new { sc.StudentId, sc.CourseId });

            modelBuilder
                .Entity<StudentCourse>()
                .HasOne(sc => sc.Student)
                .WithMany(s => s.StudentCourses)
                .HasForeignKey(sc => sc.StudentId);

            modelBuilder
                .Entity<StudentCourse>()
                .HasOne(sc => sc.Course)
                .WithMany(c => c.StudentCourses)
                .HasForeignKey(sc => sc.CourseId);
        }

    }
}
Solution to save data

Click the “Run” button in the solution above, then execute the command below in the terminal:

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dotnet run

Below is a snippet from the output:

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---DEPARTMENTS---
TITLE                   HOD
Computer Science        Fraser Jones
Business Management     Jennifer Rock
---INSTRUCTORS---
FIRSTNAME       LASTNAME        DEPARTMENT
blessing        Udoh            Computer Science
Coleman         Bale            Computer Science
Benedict        Okon            Business Management
---COURSES---
TITLE                   DEPARTMENT
Information Systems     Computer Science
Software Engineering    Computer Science
Business Leadership     Business Management
Digital Business        Business Management
---STUDENTS---
FIRSTNAME       LASTNAME        DEPARTMENT
Ferdinand       Mbotidem        Computer Science
Margaret        Olorunisola     Business Management

Solution breakdown

Let’s review the solutions highlighted in the project.

Insert department and instructor data

Lines 35–38 of SchoolContext.cs indicate that there is a one-to-many relationship between departments and instructors. For this reason, we can insert them into the database as a related graph of entities.

Note the following from ...