Use code first

Use EF Core establish Code First, Complete database migration .

Use sqlite database

1. Build a .net core web api project

2. install Microsoft.EntityFrameworkCore.Sqlite

3. Create an entity

   public class User
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public int age { get; set; }
    }

4. establish DataContext

Inherit DbContext, Initialize constructor , Inherit base, And then User Class write

    public class DataContext : DbContext
    {
        public DataContext(DbContextOptions<DataContext> options)
            : base(options)
        {

        }

        public DbSet<User> Users { get; set; }
    }

5. Configuration database  

            var connrection = "FileName=./demo.db";
            services.AddDbContext<DataContext>(options =>
            {
                options.UseSqlite(connrection);
            });

Here we can put Sqlite, Change to another database address

Be careful ： It must be written here FileName=./demo.db  Otherwise, an error will be reported when it is generated later

6. install Microsoft.EntityFrameworkCore.tools

7. To configure appsettings.json

{
  "Logging": {
    "LogLevel": {
      "Default": "Information",
      "Microsoft": "Warning",
      "Microsoft.Hosting.Lifetime": "Information"
    }
  },
  "AllowedHosts": "*",
  "tools": {
    "Microsoft.EntityFrameworkCore.Tools": {
      "version": "1.0.0-previewl-final",
      "imports": [
        "portable-net 45+win8+dnxcore50",
        "portable-net 45+win8"
      ]
    }
  }
}

8. In the package manager console , Input Add-Migration xxx

9. In the input Update-Database, Create database complete

 9. Use

Don't forget  context.SaveChanges();

using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Logging;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

namespace WebApplication6.Controllers
{
    [ApiController]
    [Route("[controller]")]
    public class WeatherForecastController : ControllerBase
    {
        private static readonly string[] Summaries = new[]
        {
            "Freezing", "Bracing", "Chilly", "Cool", "Mild", "Warm", "Balmy", "Hot", "Sweltering", "Scorching"
        };

        private readonly ILogger<WeatherForecastController> _logger;
        private readonly DataContext context;

        public WeatherForecastController(ILogger<WeatherForecastController> logger,DataContext context)
        {
            _logger = logger;
            this.context = context;
        }

        [HttpGet]
        public IEnumerable<WeatherForecast> Get()
        {
            User user = new User();
            user.age = 15;
            user.Id = 1;
            user.Name = " Zhang San ";
            context.Add(user);
            context.SaveChanges();
            var rng = new Random();

            var n = context.Users.Where(n => n.Name == " Zhang San ");
            foreach (var item in n)
            {
                Console.WriteLine(item.Name);
            }
           
            return Enumerable.Range(1, 5).Select(index => new WeatherForecast
            {
                Date = DateTime.Now.AddDays(index),
                TemperatureC = rng.Next(-20, 55),
                Summary = Summaries[rng.Next(Summaries.Length)]
            })
            .ToArray();
        }
    }
}