C#•2mo ago

duplicate key error efcore

I'm trying to use efcore but I'm getting a duplicate key value violates unique constraint "PK_Tags" error. My model contains:

        [Required]
        public List<string> Tags { get; set; } = [];

        [Required]
        public List<string> Tags { get; set; } = [];

however, this is not a key? I'm updating the value by getting it from the database, modifying it, then calling Update with the modified value.

16 Replies

Keswiik•2mo ago

Check your database schema. My guess is that Tags is being mapped to a new table.

Ruttie•2mo ago

Is keeping entries I got from the database around for a long time bad? long time as in across dbcontexts in other words, if I get value a from dbctx1, then cache a, dispose of dbctx1, create dbctx2, and use the .Update method on dbctx2 with value a I'm guessing it is a problem, and that the changetracker of dbctx2 doesn't recognize a as being modified, rather created if that's the case, am I supposed to do a new query everytime I use a new dbcontext? isn't that inefficient? ping for visibility

Keswiik•2mo ago

First off, did you look at your DB schema?

Ruttie•2mo ago

I've come to the conclusion that this is most likely unrelated

Keswiik•2mo ago

And you can keep entries around for a long time, I have caches like that in some of my projects. Not sure whether or not that's recommended, though.

Ruttie•2mo ago

the sql states an INSERT INTO instead of the UPDATE I expect when using .Update

Keswiik•2mo ago

show actual code

Ruttie•2mo ago

I have a service injecting an IMemoryCache, then have a get method:

        public DbTag? GetTag(ulong guildid, string name)
        {
            var key = new TagKey(guildid, name);
            if (cache.TryGetValue(key, out DbTag? tag))
                return tag!;
            var guild = guilds.GetOrCreateGuild(guildid);
            if (!guild.Tags.Contains(name))
                return null;
            var val = db.Tags.Find(guildid, name);
            cache.CreateEntry(key).SetValue(val).SetAbsoluteExpiration(TimeSpan.FromMinutes(30)).Dispose();
            return val;
        }

        public DbTag? GetTag(ulong guildid, string name)
        {
            var key = new TagKey(guildid, name);
            if (cache.TryGetValue(key, out DbTag? tag))
                return tag!;
            var guild = guilds.GetOrCreateGuild(guildid);
            if (!guild.Tags.Contains(name))
                return null;
            var val = db.Tags.Find(guildid, name);
            cache.CreateEntry(key).SetValue(val).SetAbsoluteExpiration(TimeSpan.FromMinutes(30)).Dispose();
            return val;
        }

after which a second call to this gets the value from cache instead of db, and then I call this:

        public void Update(ulong guild, DbTag value)
        {
            db.Tags.Update(value);
            db.SaveChanges();
        }

        public void Update(ulong guild, DbTag value)
        {
            db.Tags.Update(value);
            db.SaveChanges();
        }

on the second context which then causes an error

Keswiik•2mo ago

Show the code that calls Update

Ruttie•2mo ago

        if (tags.GetTag(guildid.Value, state) is not { } tag)
            return (Result)await feedback.SendContextualAsync("This tag does not exist! (did someone delete the tag before you could update it?)", ct: base.CancellationToken);
        tag.Content = content;
        tag.IsEmbed = true;
        tags.Update(guildid.Value, tag);

        if (tags.GetTag(guildid.Value, state) is not { } tag)
            return (Result)await feedback.SendContextualAsync("This tag does not exist! (did someone delete the tag before you could update it?)", ct: base.CancellationToken);
        tag.Content = content;
        tag.IsEmbed = true;
        tags.Update(guildid.Value, tag);

I wonder if db.Tags.Update(value).State = Microsoft.EntityFrameworkCore.EntityState.Modified; would work

Keswiik•2mo ago

You could also try tracking the entity before modifying it

Ruttie•2mo ago

is there a way to make it track something?

Keswiik•2mo ago

That's what DbSet.Update does it begins tracking an entity and sets the state to modified So I'd try calling DbSet.Update with your tag, modify the tag after, then call SaveChanges

Ruttie•2mo ago

I was wondering if I could start tracking if I can get it from the cache

Keswiik•2mo ago

So call DbSet.Update on your tags every time you load from the cache....?

Ruttie•2mo ago

but it's never modified so I was concerned the setting state to modified would break things found .Attach seems to do that did not work got it working I was being stupid thanks for dealing with it :catlaugh:

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duplicate key error efcore