C#•7mo ago

Simple AP

Hello im trying to connect c# to database and i have a slight problem with foreign keys here is my code the hierarrchy is firma-> division->project->oddelenie plus there are employes here is my code

Dokument.rtf

60 Replies

MaruOP•7mo ago

also i have this error ntroducing FOREIGN KEY constraint 'FK_DbDiviza_DbZamestnanec_VeduciDivRodneCislo' on table 'DbDiviza' may cause cycles or multiple cascade paths. Specify ON DELETE NO ACTION or ON UPDATE NO ACTION, or modify other FOREIGN KEY constraints. Could not create constraint or index. See previous errors. its my first time working with this

MaruOP•7mo ago

KrosOrg.zip

Pobiega•7mo ago

No zips or word documents please, either upload to github or similar or paste the relevant stuff on $paste

MODiX•7mo ago

If your code is too long, you can post to https://paste.mod.gg/ and copy the link into chat for others to see your shared code!

Pobiega•7mo ago

however, this is entirely a SQL problem - your database design has errors in it in this case, your foreign keys have some form of ON DELETE/UPDATE action that conflicts with another foreign key

MaruOP•7mo ago

yes that is wha the error said but i lack the knowledge on how to fix it

Pobiega•7mo ago

check what foreignkeys you have on "DbDiviza"

MaruOP•7mo ago

i have 2 idfirm and id of employe

Pobiega•7mo ago

ok so, if deleting a firm, it makes sense for a division to also be deleted. agreed? but why is there a foreign key for id of employee? or do you mean that you have a employee.DivisionId field?

MaruOP•7mo ago

oh that makes sens e i thought that division would use employe as a division leader but that seems to get rid of the problem when i dleted the leaders of divison, project ect im just gonna add into employe a boolen to set if its a leader of company,div ect

Pobiega•7mo ago

you can have a "division leader" just fine, but it needs to have ON DELETE NO ACTION

MaruOP•7mo ago

yea but i have no clue how to do that in c# XD is it like a parameter or a method or

Pobiega•7mo ago

its not related to C# at all how are you making your database?

MaruOP•7mo ago

im using entity frame work and creating it there thru migrating

Pobiega•7mo ago

Okay, now we're getting somewhere What version of EF?

MaruOP•7mo ago

8.0.5

Pobiega•7mo ago

ok good, so modern EF Core

MaruOP•7mo ago

well i did Add-Migration InitialCreate

Pobiega•7mo ago

you'd do this via the EntityConfiguration api, either via a IEntityTypeConfiguration<T> or via OnModelConfiguring

MaruOP•7mo ago

and also update-database lemme check

Pobiega•7mo ago

can you show me your database context source? preferably via $code

MODiX•7mo ago

To post C# code type the following: ```cs // code here ``` Get an example by typing $codegif in chat For longer snippets, use: https://paste.mod.gg/

MaruOP•7mo ago

wrong code

Pobiega•7mo ago

copy the URL from the pastebin 😄

MaruOP•7mo ago

XD yea

MaruOP•7mo ago

https://paste.mod.gg/iseweprgwemw/0

BlazeBin - iseweprgwemw

A tool for sharing your source code with the world!

Pobiega•7mo ago

ok so uhh not the migration I need to see the database context your migration is generated from your context + configurations so you should delete your existing DatabaseSnapshot + migration

MaruOP•7mo ago

https://paste.mod.gg/qdlvfqyrozfp/0

BlazeBin - qdlvfqyrozfp

A tool for sharing your source code with the world!

Pobiega•7mo ago

and re-create it, after we fix your context

MaruOP•7mo ago

Pobiega•7mo ago

ok, no configuration at all thats your problem I'll need to see the entities too, thats the classes that are used in your context

MaruOP•7mo ago

ok sec

Pobiega•7mo ago

just a general recommendation, its recommended to keep your code in english not everyone understands romanian 😛

MaruOP•7mo ago

its slovak but im gonna start using eng i guess

Pobiega•7mo ago

ah, close enough 😄

MaruOP•7mo ago

yea

Pobiega•7mo ago

Zamestnanec seems to be your employee, right?

MaruOP•7mo ago

yea

MaruOP•7mo ago

https://paste.mod.gg/fkufwjmhdsqy/4

BlazeBin - fkufwjmhdsqy

A tool for sharing your source code with the world!

MaruOP•7mo ago

divizia is divison projekt is project oddelenies is departement

Pobiega•7mo ago

right

MaruOP•7mo ago

firma is company

Pobiega•7mo ago

so, EF has some conventions lets say your classes were called Employee and Division if you had a EmployeeId field in Division, it would automatically understand that its a foreign key for a Employee I also strongly recommend not using attributes to configure your models and using the conventional names

MaruOP•7mo ago

okay so what do u recommend

Pobiega•7mo ago

1 sec

MaruOP•7mo ago

take ur time nothing is rushing me

Pobiega•7mo ago

using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Metadata.Builders;

namespace TestEfApp.Data;

public class MyDbContext : DbContext
{
    public MyDbContext(DbContextOptions<MyDbContext> options) : base(options)
    {
    }

    public DbSet<Division> Divisions { get; private set; }
    public DbSet<Company> Companies { get; private set; }
    public DbSet<Employee> Employees { get; private set; }


    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.ApplyConfigurationsFromAssembly(typeof(MyDbContext).Assembly);

        base.OnModelCreating(modelBuilder);
    }
}

public class DivisionConfiguration : IEntityTypeConfiguration<Division>
{
    public void Configure(EntityTypeBuilder<Division> builder)
    {
        builder
            .HasOne<Employee>(x => x.DivisionLeader)
            .WithMany()
            .HasForeignKey(x => x.DivisionLeaderId)
            .OnDelete(DeleteBehavior.SetNull);
    }
}

public class Division
{
    public int Id { get; set; }

    public int CompanyId { get; set; }

    public Company Company { get; set; }

    public string Name { get; set; }

    public int? DivisionLeaderId { get; set; }

    public Employee? DivisionLeader { get; set; }
}

public class Employee
{
    public int Id { get; set; }

    public string Name { get; set; }
}

public class Company
{
    public int Id { get; set; }

    public string Name { get; set; }
}

using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Metadata.Builders;

namespace TestEfApp.Data;

public class MyDbContext : DbContext
{
    public MyDbContext(DbContextOptions<MyDbContext> options) : base(options)
    {
    }

    public DbSet<Division> Divisions { get; private set; }
    public DbSet<Company> Companies { get; private set; }
    public DbSet<Employee> Employees { get; private set; }


    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.ApplyConfigurationsFromAssembly(typeof(MyDbContext).Assembly);

        base.OnModelCreating(modelBuilder);
    }
}

public class DivisionConfiguration : IEntityTypeConfiguration<Division>
{
    public void Configure(EntityTypeBuilder<Division> builder)
    {
        builder
            .HasOne<Employee>(x => x.DivisionLeader)
            .WithMany()
            .HasForeignKey(x => x.DivisionLeaderId)
            .OnDelete(DeleteBehavior.SetNull);
    }
}

public class Division
{
    public int Id { get; set; }

    public int CompanyId { get; set; }

    public Company Company { get; set; }

    public string Name { get; set; }

    public int? DivisionLeaderId { get; set; }

    public Employee? DivisionLeader { get; set; }
}

public class Employee
{
    public int Id { get; set; }

    public string Name { get; set; }
}

public class Company
{
    public int Id { get; set; }

    public string Name { get; set; }
}

something like this obviously not all in one file 😄 but notice how all entities have an int Id property and we can configure the divisionleader with the entity configuration

MaruOP•7mo ago

the employe the ? what does that mean or any other ?

Pobiega•7mo ago

it means nullable

MaruOP•7mo ago

Pobiega•7mo ago

it means that a division might not have a leader some do, some dont and if the leader is deleted, we automatically set this value to null to indicate that the division has no leader then

MaruOP•7mo ago

oooh okay thats why it had a problem with cascading ? or the on update no delete

Pobiega•7mo ago

yeah SQL isnt trivial, relationships must be guaranteed to always be valid and there are a ton of rules and checks in place to ensure that and that can often get confusing when you are new

MaruOP•7mo ago

yea i was kinda confused since i only worked with c++ and java so far

Pobiega•7mo ago

when I first started out with SQL 20+ years ago, we didnt have fancy tools like EF either I wrote my sql manually and just skipped foreign keys for a long time 😄

MaruOP•7mo ago

daaamn must have been hard 😄 well im happy that there are tools for that nowadays

Pobiega•7mo ago

in a way it was great tbh it means I actually know why those errors appear to be fair I love EF and would highly recommend using it but it also means the sql layer is "hidden" and when you get an error like this its not obvious what you need to do to configure it but yeah, use IEntityTypeConfiguration<T> to configure your entities, not attributes it gives you much more options

MaruOP•7mo ago

alright im gonna implement the changes after that ill have to figure out how to do front end hah

Pobiega•7mo ago

gl!

MaruOP•7mo ago

thanks a bunch

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