.NetCore之EF跳過的坑

我在網上看到很多.netCore的信息，就動手自己寫一個例子測試哈，但是想不到其中這么多坑；

1.首先.netCore和EF的安裝就不用多說了，網上有很多的講解可以跟着一步一步的下載和安裝，但是需要注意點就安裝Microsoft.EntityFrameworkCore.SqlServer程序包（Install-Package Microsoft.EntityFrameworkCore.Sqlite –Pre）；

2.創建實體

/// <summary>
    ///  學生類
    /// </summary>
    public class Student
    {
        /// <summary>
        /// ID
        /// </summary>
        [Key]
        public Guid ID { get; set; } = Guid.NewGuid();
        /// <summary>
        /// 名字
        /// </summary>
        [StringLength(50)]
        [Required]
        public string Name { get; set; }
        /// <summary>
        /// 年齡
        /// </summary>
        public int Age { get; set; }
        /// <summary>
        /// 性別
        /// </summary>
        public EmSex Sex { get; set; } = EmSex.未填;
    }
    public enum EmSex
    {
        男 = 0,
        女 = 1,
        未填 = 2
    }

3.創建EF的上下文DbContext

public class DbContextHelper : DbContext
    {
        public DbSet<Student> StudentEntity { get; set; }

        public DbContextHelper() { }

        public DbContextHelper(DbContextOptions options) : base(options)
        {
        }

        //protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        //{
        //    string str = "data source=.; Initial Catalog=NetCore_TestDB ; uid=sa; pwd=qwertyuiop";
        //    optionsBuilder.UseSqlServer(str);
        //    //optionsBuilder.UseSqlite(str);
         
        //}
    }

4.編寫數據庫操作的接口和實現類

 public interface IStudentService
    {
        Task<int> AddStudnet(Student entity);
        Task<int> DeltStudent(Guid id);
       List<Student> GetStudent(Expression<Func<Student,bool>> fun);
    }
public class StudentService : IStudentService
    {
        public  async Task<int> AddStudnet(Student entity)
        {
            using (DbContextHelper dbHelper =new DbContextHelper () ) {
                await dbHelper.AddAsync(entity);
                return dbHelper.SaveChanges();
            }
        }
        public async Task<int> DeltStudent(Guid id)
        {
            using (DbContextHelper dbHelper =new DbHelper.DbContextHelper ()) {
                var entity =await dbHelper.StudentEntity.FindAsync(id);
                if (entity == null)
                {
                    return -1;
                }
                else
                {
                    dbHelper.StudentEntity.Remove(entity);
                    return dbHelper.SaveChanges();
                }
            }
        }
        public List<Student> GetStudent(Expression<Func<Student, bool>> fun)
        {
            using (DbContextHelper dbHelper =new DbHelper.DbContextHelper ()) {
                var List = dbHelper.StudentEntity.Where(fun).ToList();
                return List;
            }
        }
    }

5.創建Controller進行調用

public class HomeController : Controller
    {
        private IStudentService StudentDb = new StudentService();
        // GET: /<controller>/
        public IActionResult Index()
        {
            var  list = StudentDb.GetStudent(it=>true);
            return View();
        }
    }

6.下面配置數據庫鏈接和EF的初始化創建

public void ConfigureServices(IServiceCollection services)
        {
            // Add framework services.
            services.AddApplicationInsightsTelemetry(Configuration);

            //services.AddEntityFrameworkSqlServer()
            //    .AddDbContext<DbContextHelper>();
            //options =>
           // options.UseSqlServer(Configuration["AppSettings:DefaultConnectionStr"])
            services.AddDbContext<DbContextHelper>(options => options.UseSqlite(Configuration["AppSettings:DefaultConnectionStr"]));


            services.AddMvc();
            services.AddTransient<IStudentService, StudentService>();
        }

"AppSettings": {
    "DefaultConnectionStr": "data source=.; Initial Catalog=NetCore_TestDB ; uid=sa; pwd=qwertyuiop"
  },

上面很多網上都有相關的資料可以查詢，我這里只是梳理了哈，下面開始運行

開始報這個錯誤

后面經過查看很多資料，曉得是上下文的注冊造成的，這個問題就需要注意幾點：

1.獲取字符串一定要注意不要不能包含空格符號

services.AddDbContext<DbContextHelper>(options => options.UseSqlite(Configuration["AppSettings:DefaultConnectionStr"]));

2.一定給要注意區分哈UseSqlite和UseSqlServer；

修改之后運行，還是會有上面的問題，具體原因我也不是很清楚，但是我找寧外一種解決方案進行初始化數據庫鏈接字符串，重寫OnConfiguring

protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            string str = "data source=.; Initial Catalog=NetCore_TestDB ; uid=sa; pwd=qwertyuiop";
            optionsBuilder.UseSqlServer(str);
        }

修改之后在運行，問題得到了解決。

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