Can#39;t auto-generate IDENTITY with AddRange in Entity Framework(无法在实体框架中使用 AddRange 自动生成 IDENTITY)

本文介绍了无法在实体框架中使用 AddRange 自动生成 IDENTITY的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！

问题描述

我不知道这是实体框架的设计选择还是代表我的错误方法，但每当我尝试将实体添加到 DbSet 时，我似乎都无法获得自动生成的 IDENTITY 字段.

I don't know if it's an Entity Framework's desing choice or a wrong approach on my behalf, but whenever I try to AddRange entities to a DbSet I can't seem to get the auto-generated IDENTITY fields.

[Table("entities")]
public class Entity 
{
    [Key]
    [Column("id")]
    public long Id { get; set; }

    [Column("field")]
    public string Field { get; set; }
}

var entities = new Entity[] 
{
    new Entity() { Field = "A" },
    new Entity() { Field = "B" },
};

_dbContext.Entities.AddRange(entities);
await _dbContext.SaveChangesAsync();

//ids are still default(long) at this point!!

这是更新的代码以显示导致问题的原因:enumerables.无需在实体类中添加其他属性.

Here's the updated code to show what was causing the problem: enumerables. No need to add other attributes to the entity classes.

public class Request
{
    public string Field { get; set; }

    public Entity ToEntity()
    {
        return new Entity() { Field = Field };
    }
}

public async Task<IEnumerable<long>> SaveRequests(IEnumerable<Request> requests)
{
    var entities = requests.Select(r => r.ToEntity()); //not working
    var entities = requests.Select(r => r.ToEntity()).ToArray(); //working

    _dbContext.Entities.AddRange(entities);
    await _dbContext.SaveChangesAsync();

    return entities.Select(e => e.Id);
}

推荐答案

是什么导致了问题?可数！请查看我的问题中的 EDIT 部分以获取解决方案.

What was causing the problem? Enumerables! Take a look at the EDIT section in my question for the solution.

在此处发布更新的代码作为答案.问题在于我使用枚举的方式.最重要的是，当您需要立即获得一致的结果时，您永远不应该相信延迟加载.

posting the updated code here as answer. The problem was in the way I used enumerables. Bottom line is you should never trust lazy loading when you need consistent results right away.

public class Request
{
    public string Field { get; set; }

    public Entity ToEntity()
    {
        return new Entity() { Field = Field };
    }
}

public async Task<IEnumerable<long>> SaveRequests(IEnumerable<Request> requests)
{
    var entities = requests.Select(r => r.ToEntity()); //not working
    var entities = requests.Select(r => r.ToEntity()).ToArray(); //working

    _dbContext.Entities.AddRange(entities);
    await _dbContext.SaveChangesAsync();

    return entities.Select(e => e.Id);
}

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