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EF Core Database First Discover How to Create Model From Database
In the previous article, we have seen the migrations to create a database from a DbContext and classes. It is also possible to reverse engineer an existing database into a DbContext and classes, and it is known as Database First approach.
- We have a simple database created in the previous article, and it contains two tables,
OrderandOrderDetail. - To create a DbContext and classes from the existing database, we will run the
Scaffold-DbContextcommand in Package Manager console.
Let's create a new empty project and add all the required packages for EF core which is explained in the Code First approach.
Now we need to run the scaffold-dbcontext command with just the required parameters.
PM> Scaffold-DbContext -Provider Microsoft.EntityFrameworkCore.SqlServer -Connection "Data Source=(localdb)\ProjectsV13;Initial Catalog=StoreDB;"
The provider and connection parameters are required, the provider is Microsoft.EntityFrameworkCore.SqlServer and the connection is the connection string for our legacy database.
When you run this command, a bunch of new files is added in the Solution Explorer.
Now let's look at the new DbContext class.
public partial class StoreDBContext : DbContext { public virtual DbSet<OrderDetails> OrderDetails { get; set; } public virtual DbSet<Orders> Orders { get; set; } protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder) { if (!optionsBuilder.IsConfigured) { #warning To protect potentially sensitive information in your connection string, you should move it out of source code. See https://go.microsoft.com/fwlink/?LinkId=723263 for guidance on storing connection strings. optionsBuilder.UseSqlServer(@"Data Source=(localdb)\ProjectsV13;Initial Catalog=StoreDB;"); } } protected override void OnModelCreating(ModelBuilder modelBuilder) { modelBuilder.Entity<OrderDetails>(entity => { entity.HasKey(e => e.OrderDetailId); entity.HasIndex(e => e.OrderId); entity.Property(e => e.OrderDetailId).HasColumnName("OrderDetailID"); entity.Property(e => e.OrderId).HasColumnName("OrderID"); entity.Property(e => e.ProductId).HasColumnName("ProductID"); entity.HasOne(d => d.Order) .WithMany(p => p.OrderDetails) .HasForeignKey(d => d.OrderId); }); modelBuilder.Entity<Orders>(entity => { entity.HasKey(e => e.OrderId); entity.Property(e => e.OrderId).HasColumnName("OrderID"); entity.Property(e => e.CustomerId).HasColumnName("CustomerID"); entity.Property(e => e.EmployeeId).HasColumnName("EmployeeID"); }); } }
- You can see that DbSet properties are created for every one of the Entity classes.
- It also put the connection string directly in the OnConfiguring method with a note that you might not want it there for security reasons.
- There are also a bunch of explicit fluent mappings for the indexes and relationship etc.
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