C#•8mo ago

❔ EF blowing up trying to insert a relationship that already exists

Code and question are in the text file

message.txt

15 Replies

var thing = context.Things.Single(t => t.Id == 1);

var thingCopy = new Thing()
{
    Name = thing.Name,
    Attributes = thing.Attributes
};

var thing = context.Things.Single(t => t.Id == 1);

var thingCopy = new Thing()
{
    Name = thing.Name,
    Attributes = thing.Attributes
};

don't do this this is not how EF works this is you telling EF to create a new Thing record, not to update an existing Thing record

Matney•8mo ago

In that thingCopy is a new Thing record? I know that much... I probably should have specified that I'm doing that to bind thingCopy to some Blazor components, and I want to be able to Cancel out without modifying the original thing object. Is it possible to revert changes on an unsaved EF entity?

JakenVeina•8mo ago

Cancel out without modifying the original thing object

in what regard? if you don't want to modify the original Thing object, then don't never expose it to the UI

Matney•8mo ago

Yeah, I'm not -- that's what the copy is for.

JakenVeina•8mo ago

the copy is for the UI?

Matney•8mo ago

Yeah

JakenVeina•8mo ago

then why are you trying to save it?

Matney•8mo ago

I want to save the changes made to the copy -- as a potentially discardable stand-in for the original thing -- back to the original thing record.

JakenVeina•8mo ago

then save changes made to the copy

Matney•8mo ago

That's what I'm trying to do

JakenVeina•8mo ago

public async Task OnSaveButtonClickedAsync()
{
    using var context = _contextFactory.CreateDbContext();
    var thing = context.Things.Find(_currentThing.Id);

    thing.Name = _currentThing.Name;

    var existingAttributes = await context.Attributes
        .Where(attribute => attribute.ThingId == _currentThing.Id)
        .ToListAsync();

    foreach(var attribute in _currentThing.Attributes)
        if (!existingAttributes.Any(existingAttribute => existingAttribute.Name == attribute.Name))
            context.Attributes.Add(new Attribute()
            {
                Name = attribute.Name,
                ThingId = _currentThing.Id
            });

    foreach(var existingAttribute in existingAttributes)
        if (!_currentThing.Attributes.Any(attribute => attribute.Name == existingAttribute.Name))
            context.Attributes.Remove(existingAttribute);

    await context.SaveChangesAsync();
}

public async Task OnSaveButtonClickedAsync()
{
    using var context = _contextFactory.CreateDbContext();
    var thing = context.Things.Find(_currentThing.Id);

    thing.Name = _currentThing.Name;

    var existingAttributes = await context.Attributes
        .Where(attribute => attribute.ThingId == _currentThing.Id)
        .ToListAsync();

    foreach(var attribute in _currentThing.Attributes)
        if (!existingAttributes.Any(existingAttribute => existingAttribute.Name == attribute.Name))
            context.Attributes.Add(new Attribute()
            {
                Name = attribute.Name,
                ThingId = _currentThing.Id
            });

    foreach(var existingAttribute in existingAttributes)
        if (!_currentThing.Attributes.Any(attribute => attribute.Name == existingAttribute.Name))
            context.Attributes.Remove(existingAttribute);

    await context.SaveChangesAsync();
}

Matney•8mo ago

Thank you. 😄

JakenVeina•8mo ago

this highlights the fact that you shouldn't be using Thing as your data model for the UI that's your data model for storage

Matney•8mo ago

Fair

Accord•8mo ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

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❔ EF blowing up trying to insert a relationship that already exists