iot/labs/EFCoreTest/MyDbContext.cs

using Microsoft.EntityFrameworkCore;
using System;
using System.Linq;

namespace EFCoreTest
{
    public class MyDbContext : DbContext
    {
        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            //optionsBuilder.UseSqlite("Data Source=data.db;");
            //optionsBuilder.UseMySql("Server=139.180.143.95;Port=3306;Database=test;Uid=admin;Pwd=admin;");
            ///https://www.cockroachlabs.com/docs/stable/build-a-csharp-app-with-cockroachdb.html
            /// cockroach start --insecure --host=localhost --http-port=9090
            /// cockroach sql --insecure
            /// CREATE DATABASE test;
            /// DROP DATABASE test CASCADE;
            /// \q
            optionsBuilder.UseNpgsql("User ID=root;Host=localhost;Port=26257;Database=test;");
        }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            foreach (var entity in modelBuilder.Model.GetEntityTypes())
            {
                if (entity.GetProperties().Any(o => o.Name == "Id"))
                {
                    modelBuilder.Entity(entity.Name).HasKey("Id");
                    modelBuilder.Entity(entity.Name).Property("Id").ValueGeneratedNever();
                }
                if (entity.GetProperties().Any(o => o.Name == "RowVersion"))
                {
                    modelBuilder.Entity(entity.Name).Property("RowVersion")?.IsConcurrencyToken().ValueGeneratedNever();
                }
            }
            modelBuilder.Entity<User>().Property(o => o.UserName).IsRequired().HasMaxLength(64);
            modelBuilder.Entity<Role>().Property(o => o.Name).IsRequired().HasMaxLength(64); ;
            modelBuilder.Entity<UserRole>().HasOne(o => o.User).WithMany(o => o.UserRoles).HasForeignKey(o => o.UserId);
            modelBuilder.Entity<UserRole>().HasOne(o => o.Role).WithMany(o => o.UserRoles).HasForeignKey(o => o.RoleId);
            modelBuilder.Entity<UserRole>().HasIndex(o => new { o.UserId, o.RoleId }).IsUnique();
        }

        public override int SaveChanges()
        {
            var entries = this.ChangeTracker.Entries().ToList();
            foreach (var entry in entries)
            {
                if (entry.State == EntityState.Added || entry.State == EntityState.Modified)
                {
                    var now = DateTime.UtcNow;
                    if (entry.State == EntityState.Added)
                    {
                        if (entry.Properties.Any(o => o.Metadata.Name == "Created"))
                        {
                            entry.Property("Created").CurrentValue = now;
                        }
                    }
                    if (entry.Properties.Any(o => o.Metadata.Name == "RowVersion"))
                    {
                        entry.Property("RowVersion").CurrentValue = Guid.NewGuid().ToString();
                    }
                    if (entry.Properties.Any(o => o.Metadata.Name == "LastChanged"))
                    {
                        entry.Property("LastChanged").CurrentValue = now;
                    }
                }
                Console.WriteLine($"id:{entry.Entity.ToString()},state:{entry.State}");
            }
            return base.SaveChanges();
        }
    }
}