Entity framework core lazy loading not performed when inserting new instances

Question

I have two classes:

Campaign which references a class customer:

public class Campaign
{
    [Key]
    [Required]
    public int id { get; set; }
    public int? CustomerId { get; set; }
    [ForeignKey("CustomerId")]
    public virtual Customer customer { get; set; }
}

And Customer:

public class Customer
{
    [Key]
    [Required]
    public int id { get; set; }
    [Required]
    public string name { get; set; }
    [Required]
    public double turnover { get; set; }
    public virtual ICollection<Campaign> campaigns { get; set; }
}

Here's is an insert method:

async Task<Campaign> ICampaignRepository.InsertCampaign(Campaign campaign)
{
    try
    {
        _context.Campaigns.Add(campaign);
        await _context.SaveChangesAsync();
        return campaign;
    }
    catch (Exception)
    {
        throw;
    }
}

I'm using Microsoft.EntityFrameworkCore.Proxies package for lazy loading.

After adding a campaign instance having a customerId, the customer is not lazy loaded in the inserted object. Please note that I tried to fetch the campaign by id before returning it, but the problem persists, and I want to avoid loading the customer explicitly.

Lazy loading is perfectly working when performing fetch operations on existing records.

EF Core isn’t lazy loading anything by default (that’s a good thing btw.), and I don’t think automatically loading related things on added entities is supported at all. — poke
– poke, Commented Jul 24, 2019 at 10:47
I'm using Microsoft.EntityFrameworkCore.Proxies package for lazy loading — khalil
– khalil, Commented Jul 24, 2019 at 11:00
The entity you get passed to your function very likely isn’t a proxy entity though. So the lazy loading magic won’t happen there. You might need to create the object with _context.CreateProxy(). — poke
– poke, Commented Jul 24, 2019 at 11:07
_context.CreateProxy() should be called to create the parent object or the navigation property ? — khalil
– khalil, Commented Jul 24, 2019 at 11:14

poke · Accepted Answer · 2019-07-25 10:07:42Z

12

Thanks to poke

The solution is to:

Create a proxy for your entity using CreateProxy:

Campaign toCreate = _context.Campaigns.CreateProxy();

Transfer new values to your proxy object:

_context.Entry(toCreate).CurrentValues.SetValues(Campaign);

Finally, save your proxy object to the context:

_context.Add(toCreate);
await _context.SaveChangesAsync();`

Here's the full method:

async Task<Campaign> ICampaignRepository.InsertCampaign(Campaign campaign)
{
    Campaign toCreate = _context.Campaigns.CreateProxy();
    _context.Entry(toCreate).CurrentValues.SetValues(campaign);
    _context.Add(toCreate);
    await _context.SaveChangesAsync();
    return toCreate;
}

edited Jul 25, 2019 at 10:07

poke

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answered Jul 24, 2019 at 14:45

khalil

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1 Comment

Ted Chirvasiu Over a year ago

Just a heads up for anyone trying this, if Campaign in your case contains collections you may wanna double check if _context.Entry(toCreate).CurrentValues.SetValues(campaign) actually assigns the collections. In my case it silently didn't, could be because I am on an older version (EF Core 3.1.32) or something local, not sure. But I used a mapper (AutoMapper in my case) to do the assignment of values from the object to the proxy. Something like: Campaign toCreate = _context.Campaigns.CreateProxy(); _context.Add(toCreate); Mapper.Map(campaign, toCreate);

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