当我尝试使用EF db上下文从数据库中获取实体时,我有NullReferenceException:
这是我的测试代码:
// it works fine
using (var sql = new SqlConnection("--here is my connection string--"))
{
sql.Open();
var cmd = sql.CreateCommand();
cmd.CommandText = "select field1, field2 from my_table";
var reader = cmd.ExecuteReader();
reader.Read();
// here is true value
var val = reader.GetValue(0);
}
// failed
var ctx = new BackupDbContext();
var query = ctx.Database.SqlQuery<MyEntity>("select field1, field2 from my_table");
var res = query.ToList(); // NullReferenceException
// failed
var tt = ctx.MyEntities.ToList(); // NullReferenceException
我的DbContext和映射:
public class MyEntityMapping : EntityTypeConfiguration<MyEntity>
{
public MyEntityMapping()
{
ToTable("my_table");
HasKey(p => p.Field1);
Property(p => p.Field1).HasColumnName("field1");
Property(p => p.Field2).HasColumnName("field2");
}
}
public class BackupDbContext: DbContext
{
static BackupDbContext()
{
Database.SetInitializer<BackupDbContext>(null);
}
public BackupDbContext():base("name=BackupDbContext")
{
Database.Log = sql => Debug.Write(sql);
}
public virtual DbSet<MyEntity> MyEntities { get; set; }
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.HasDefaultSchema("dbo");
modelBuilder.Configurations
.Add(new MyEntityMapping());
}
}
我不知道异常的原因是什么。
我有以下堆栈跟踪:
有谁知道为什么会这样或者能给我一个暗示?
修改
连接: ...
<connectionStrings>
<add name="BackupDbContext" connectionString="Data Source=My_datasource;Encrypt=False;Initial Catalog=my_db;Integrated Security=True;" providerName="System.Data.SqlClient" />
</connectionStrings>
答案 0 :(得分:0)
您应该在webconfig文件中定义一个ConnectionString。
<connectionStrings>
<add name="DefaultConnection" connectionString="Data Source=Your server nane;Initial Catalog=Your database name;Integrated Security=True"
providerName="System.Data.SqlClient" />
</connectionStrings>
然后你必须在DbContext中使用它
public BackupDbContext():base("DefaultConnection")
{
Database.Log = sql => Debug.Write(sql);
}
现在这句话应该有效。
var ctx = new BackupDbContext();
var tt = ctx.MyEntities.ToList();