code first 创建和初始化数据库

1.前言　

　Code First是Entity Framework提供的一种新的编程模型。通过Code First我们可以在还没有建立数据库的情况下就开始编码，然后通过代码对象来生成数据库。当然我们在实际开发过程当中要做单元测试。进而每次测试的时候 要对库进行初始化，这样就不会因上次测试而对本次测试有所影响。下面是具体的实现。

2.建立对象

2.1建立对象

    /// <summary>
    /// model对象
    /// </summary>
    public class model_item : supermodel
    {
        public model_item()
        {
            type = ItemType.Normal;//枚举类型初始化
        }

        [Required]
        [StringLength(, MinimumLength = )]
        public string name { get; set; }
        [Required]
        [StringLength(, MinimumLength = )]
        public string code { get; set; }
        public ItemType type { get; set; }
        public bool State { get; set; }
        public string Icon { get; set; }
        public long sort { get; set; }
        public long appid { get; set; }
    }

2.2.DBContext

public class GDG_DbContext : DbContext
    {
        public GDG_DbContext() : base("GDG_DbContext") { }
        public DbSet<model_item> model_item { get; set; }
       protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            base.OnModelCreating(modelBuilder);
            modelBuilder.Conventions.Remove<PluralizingTableNameConvention>();

        }
    }

2.3为对象赋默认值【可选择】

public class DataInit : IDataInitializer<GDG_DbContext>    {

　　　　public void Initialize(GDG_DbContext context)
       　　 {
              List<model_item> fim = new List<model_item>() {
                new model_item(){name="郭德纲",code="gdg",type= ItemType.Normal,State=true,Icon="taoxin.png",sort=0,appid=0,reg_time=DateTime.Now},
                new model_item(){name="于谦",code="yq",type= ItemType.Normal,State=true,Icon="juanmao.png",sort=1,appid=1,reg_time=DateTime.Now},
                new model_item(){name="德云社",code="dys",type= ItemType.Normal,State=true,Icon="yun.png",sort=2,appid=2,reg_time=DateTime.Now},
           };
           fim.ForEach(o => context.model_item.Add(o));
           context.SaveChanges();
        }}

3.EF Code First

3.1新增

public bool Build()
        {
            try
            {
                var context = new FeeDbContext();
                if (!context.Database.Exists())
                {
                    new List<IDataInitializer<GDG_DbContext>>() {
                        new DataInit()
                    }.Setup<GDG_DbContext>(context);
                    return true;
                }
                return false;
            }
            catch (DbEntityValidationException ex)
            {
                StringBuilder error = new StringBuilder();
                foreach (var item in ex.EntityValidationErrors)
                {
                    foreach (var item2 in item.ValidationErrors)
                    {
                        error.Append(string.Format("{0}:{1}\r\n", item2.PropertyName, item2.ErrorMessage));
                    }
                }
                Console.WriteLine("数据库初始化报错：" + error);
                throw ex;
            }
            catch (Exception e)
            {
                Console.WriteLine("数据库初始化报错：" + e.Message);
                throw e;
            }
        }

3.2移除

public bool Remove()
        {
            var context = new GDG_DbContext();
            try
            {
                if (context.Database.Exists())
                {
                    return context.Database.Delete();
                }
                return true;
            }
            catch (Exception e)
            {
                Console.WriteLine("数据库初始化报错：" + e.Message);
                return false;
            }
            finally { context.Dispose(); }
        }

3.3初始化

public bool Rebuild()
        {
            return Remove() && Build();
        }