实体框架可以查询数据但不能保存

Question

I am using EF5 and I have some entities that I wrote myself and also wrote a function that adds all the mappings to the modelbuilder configurations.

Running a simple test query, I can query items from a table successfully but when I try to add a new item and save, I get an exception that the primary key of my entity is null, even though I gave it a value.

It's quite possible that I messed up the mappings, but I don't know why it would work for a query and not a save.

public class User : IMappedEntity 
{
    [Key]
    [Column("USER_ID")]
    public int UserID { get; set; }

    [Column("FIRST_NAME")]
    public String FirstName { get; set; }

    [Column("LAST_NAME")]
    public String LastName { get; set; }

}

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
        modelBuilder.Conventions.Remove<System.Data.Entity.ModelConfiguration.Conventions.PluralizingEntitySetNameConvention>();
        modelBuilder.Conventions.Remove<System.Data.Entity.ModelConfiguration.Conventions.PluralizingTableNameConvention>();

    var addMethod = (from m in (modelBuilder.Configurations).GetType().GetMethods()
                     where m.Name == "Add" 
                        && m.GetParameters().Count() == 1
                        && m.GetParameters()[0].ParameterType.Name == typeof(EntityTypeConfiguration<>).Name
                     select m).First();

    if(mappings != null)
    {
        foreach(var map in mappings)
        {
            if(map != null && !mappedTypes.Contains(map.GetType()))
            {
                var thisType = map.GetType();

                if (thisType.IsGenericType)
                {
                    thisType = map.GetType().GenericTypeArguments[0];
                }

                var thisAddMethod = addMethod.MakeGenericMethod(new[] {thisType});
                thisAddMethod.Invoke(modelBuilder.Configurations, new[] { map });
                mappedTypes.Add(map.GetType());
            }
        }
    }
}

private List<Object> BuildMappings(IEnumerable<Type> types)
{
    List<Object> results = new List<Object>();

    var pkType = typeof(KeyAttribute);
    var dbGenType = typeof(DatabaseGeneratedAttribute);

    foreach (Type t in types)
    {
        String tableName = GetTableName(t);
        String schemaName = GetSchema(t);
        var mappingType = typeof(EntityTypeConfiguration<>).MakeGenericType(t);
        dynamic mapping = Activator.CreateInstance(mappingType);

        if (!String.IsNullOrWhiteSpace(schemaName))
           mapping.ToTable(tableName, SchemaName.ToUpper());
        else
           mapping.ToTable(tableName);

        var keys = new List<PropertyInfo>();

        foreach (PropertyInfo prop in t.GetProperties())
        {
            String columnName = prop.Name;

            if(Attribute.IsDefined(prop, typeof(ColumnAttribute)))
            {
                columnName  = (prop.GetCustomAttribute(typeof(ColumnAttribute)) as ColumnAttribute).Name;
            }

            if(Attribute.IsDefined(prop, pkType))
               keys.Add(prop);

            var genFunc = (typeof(Func<,>)).MakeGenericType(t, prop.PropertyType);
            var param = Expression.Parameter(t, "t");
            var body = Expression.PropertyOrField(param, prop.Name);
            dynamic lambda = Expression.Lambda(genFunc, body, new ParameterExpression[] { param });

            //if (prop.PropertyType == typeof(Guid) || prop.PropertyType == typeof(Nullable<Guid>))
            //{
            //    mapping.Property(lambda).HasColumnType("Guid");
            //}
            //else
            mapping.Property(lambda).HasColumnName(columnName);

            if (Attribute.IsDefined(prop, dbGenType))
               mapping.Property(lambda).HasDatabaseGeneratedOption(DatabaseGeneratedOption.Computed);
        }

        if (keys.Count == 0)
           throw new InvalidOperationException("Entity must have a primary key");
        dynamic entKey = null;

        if(keys.Count == 1)
        {
            var genFunc = (typeof(Func<,>)).MakeGenericType(t, keys[0].PropertyType);
            var param = Expression.Parameter(t, "t");
            var body = Expression.PropertyOrField(param, keys[0].Name);
            entKey = Expression.Lambda(genFunc, body, new ParameterExpression[] { param });
        }
        else
        {
            //if entity uses a compound key, it must have a function named "GetPrimaryKey()" which returns Expression<Func<EntityType,Object>>
            //this is because I can't create an expression tree that creates an anonymous type
            entKey = t.GetMethod("GetPrimaryKey");
        }

        mapping.HasKey(entKey);

        results.Add(mapping);
    }

    return results;
}

static void Main(string[] args)
{
    using (var ctx = new DQSA.Data.DBContext("DQSATEST"))
    {
        var xxx = (from u in ctx.Query<DQSA.Data.Entities.User>()
                   select u).ToList(); //this works, I can see my user

        ctx.Set<DQSA.Data.Entities.User>().Add(new DQSA.Data.Entities.User()
            { UserID = 0,
              FirstName="Sam",
              LastName="Sam"
            });

        ctx.SaveChanges(); //get an exception here

        xxx = (from u in ctx.Query<DQSA.Data.Entities.User>()
               select u).ToList();
    }
}

Answer 1

It looks like your UserID property is being mapped as an Identity column by convention so the EF query provider thinks it doesn't need to insert that value and the database complains because the field is not nullable.

You can override the convention in your model by using the DatabaseGeneratedAttribute ...

public class User : IMappedEntity 
{
    [Key]
    [Column("USER_ID")]
    [DatabaseGenerated(DatabaseGeneratedOption.None)]
    public int UserID { get; set; }

    ...
}

or by removing the convention globally (in your DbContext's OnModelCreating() method) ...

modelBuilder.Conventions.Remove<StoreGeneratedIdentityKeyConvention>();

Answer 2

我认为您需要尝试使用一个或几个记录然后使用context.SaveChanges（）作为种子。

Answer 3

by default, entity framework should mark the primary key column of a new table created with Code First as an identity column. Did the database exist prior to your code, or did you use code first to create it?

Can you verify in Management Studio that the column has identity turned on for that field?