NejCommon.NET/Models/CommonDbContext.cs

using System.Globalization;
using System.Linq.Expressions;
using System.Reflection;
using AutoMapPropertyHelper;
using EntityFrameworkCore.Projectables;
using Microsoft.AspNetCore.Http.HttpResults;
using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.ChangeTracking.Internal;
using Microsoft.EntityFrameworkCore.Infrastructure;
using Microsoft.EntityFrameworkCore.Proxies.Internal;
using Microsoft.EntityFrameworkCore.Query;
using Microsoft.EntityFrameworkCore.Storage;

namespace NejCommon.Models;


public abstract class CommonDbContext : DbContext
{
    public CommonDbContext() : base()
    {
    }
    public CommonDbContext(DbContextOptions options)
        : base(options)
    {
    }

    public abstract CommonDbContext CreateCopy();

    public async Task<bool> ApiSaveChangesAsync()
    {
        try
        {
            await SaveChangesAsync();
            return true;
        }
        catch (Exception ex)
        {
            Console.WriteLine("Error saving db: " + ex.Message);
            Console.WriteLine(ex.StackTrace);
            return false;
        }
    }

    public static BadRequest<Error> SaveError = TypedResults.BadRequest(new Error
    {
        Message = "Error saving data to database"
    });

    public async Task<Results<BadRequest<Error>, T1>> ApiSaveChangesAsync<T1>(T1 value) where T1 : IResult
    {
        var res = await ApiSaveChangesAsync();

        if (res)
            return value;
        else
            return SaveError;
    }
    public async Task<Results<BadRequest<Error>, CreatedAtRoute<T2>>> ApiSaveChangesAsyncCreate<T1, T2>(IServiceProvider providers, T1 value, bool apply = true, T2? response = null) where T2 : class, IAutomappedAttribute<T1, T2>, new()
    {
        if (response == null)
            response = new T2();
        if (!apply)
            return TypedResults.CreatedAtRoute((T2)response.ApplyFrom(providers, (object)value));

        var res = await ApiSaveChangesAsync();

        if (res)
            return TypedResults.CreatedAtRoute((T2)response.ApplyFrom(providers, (object)value));
        else
            return SaveError;
    }
    public async Task<Results<BadRequest<Error>, Ok<T2>>> ApiSaveChangesAsyncOk<T1, T2>(IServiceProvider providers, T1 value, bool apply = true, T2? response = null) where T2 : class, IAutomappedAttribute<T1, T2>, new()
    {
        if (response == null)
            response = new T2();
        if (!apply)
            return TypedResults.Ok((T2)response.ApplyFrom(providers, (object)value));

        var res = await ApiSaveChangesAsync();

        if (res)
            return TypedResults.Ok((T2)response.ApplyFrom(providers, (object)value));
        else
            return SaveError;
    }
    public async Task<Results<BadRequest<Error>, Ok<List<T2>>>> ApiSaveChangesAsyncOk<T1, T2>(IServiceProvider providers, IEnumerable<T1> value, bool apply = true, T2? response = null) where T2 : class, IAutomappedAttribute<T1, T2>, new()
    {
        if (response == null)
            response = new T2();
        if (!apply)
            return TypedResults.Ok(value.Select(x => new T2().ApplyFrom(providers, x)).ToList());

        var res = await ApiSaveChangesAsync();

        if (res)
            return TypedResults.Ok(value.Select(x => new T2().ApplyFrom(providers, x)).ToList());
        else
            return SaveError;
    }
    public async Task<Results<BadRequest<Error>, Ok>> ApiSaveChangesAsyncOk()
    {
        var res = await ApiSaveChangesAsync();

        if (res)
            return TypedResults.Ok();
        else
            return SaveError;
    }
    public async Task<T> FindOrCreateAsync<T>(Expression<Func<T, bool>> predicate, Func<T> factory) where T : class
    {
        var entity = ChangeTracker.Entries<T>().Select(x => x.Entity).FirstOrDefault(predicate.Compile());

        //find in currentDb
        if (entity == null)
        {
            entity = await Set<T>().FirstOrDefaultAsync(predicate);
        }

        //find in change tracker
        if (entity != null && Entry(entity).State == EntityState.Deleted)
        {
            /*
            Entry(entity).State = EntityState.Modified;
            Attach(entity);*/
            Entry(entity).State = EntityState.Detached;

            entity = await Set<T>().FirstOrDefaultAsync(predicate);
        }

        //find in up-to-date db
        if (entity == null)
        {
            var newAppDB = CreateCopy();

            entity = await newAppDB.Set<T>().FirstOrDefaultAsync(predicate);

            //track the entity if it's not null and not already being tracked
            if (entity != null && this.Entry(entity).State == EntityState.Detached)
                Attach(entity);
        }

        //create if not found
        if (entity == null)
        {
            var newEntity = factory();
            await this.AddAsync(newEntity);
            entity = newEntity;
        }

        return entity;
    }
    public T FindOrCreate<T>(Expression<Func<T, bool>> predicate, Func<T> factory) where T : class
    {
        var entity = ChangeTracker.Entries<T>().Where(e => e.State != EntityState.Deleted).Select(x => x.Entity).FirstOrDefault(predicate.Compile());

        //find in change tracker
        if (entity != null && Entry(entity).State == EntityState.Deleted)
        {
            Entry(entity).State = EntityState.Modified;
        }

        //find in currentDb
        if (entity == null)
        {
            entity = Set<T>().FirstOrDefault(predicate);
        }

        //find in up-to-date db
        if (entity == null)
        {
            var newAppDB = CreateCopy();

            entity = newAppDB.Set<T>().FirstOrDefault(predicate);
            if (entity != null)
                Attach(entity);
        }

        //create if not found
        if (entity == null)
        {
            var newEntity = factory();
            this.Add(newEntity);
            entity = newEntity;
        }

        return entity;
    }

    public T Create<T, TParent>(TParent parentI, string navigationName, Action<T> config = null, params object[] constructorArguments) where T : class, new() where TParent : class
    {
        var candidates = Model
            .GetEntityTypes()
            .Where(x => x.ClrType == typeof(TParent))
            .FirstOrDefault();
        var nav = candidates?.FindNavigation(navigationName);
        var entityT = nav?.TargetEntityType;

        if (entityT == null || entityT.IsOwned())
        {
            /*
                    var source = this.GetService<IStructuralTypeMaterializerSource>();

                    var materializer =
                        source.GetEmptyMaterializer(entityT);

                    var materializationContext =
                        new MaterializationContext(
                            ValueBuffer.Empty,
                            this);

                    var val = (T)materializer(materializationContext);
      */

            var factory = this.GetService<IProxyFactory>();

            var val = (T)factory.CreateProxy(
                this,
                entityT,
                constructorArguments);

            if (!nav.IsCollection)
            {
                var refVal = Entry(parentI).Reference(navigationName);
                refVal.CurrentValue = val;
                if (refVal.TargetEntry == null)
                    throw new Exception();

                refVal.TargetEntry.State = EntityState.Added;
            }

            //this.ChangeTracker.DetectChanges();

            /*
                        var refVal = this.Set<TParent>()
                            .Entry(parentI)
                            .Reference(navigationName);

                        refVal.CurrentValue = val;

                        Attach(val);

                        if (refVal.TargetEntry == null)
                            throw new Exception("test");
            */

            config?.Invoke(val);
            return val;
        }

        var entity = this.Set<T>(entityT.Name).CreateProxy(constructorArguments);

        config?.Invoke(entity);
        this.Add(entity);
        this.ChangeTracker.DetectChanges();
        return entity;
    }
    public T Create<T>(Action<T> config = null, params object[] constructorArguments)
    {
        var entity = this.CreateProxy<T>(constructorArguments);

        config?.Invoke(entity);
        this.Add(entity);
        this.ChangeTracker.DetectChanges();
        return entity;
    }
    public object Create(Type entityType, Action<object> config = null, params object[] constructorArguments)
    {
        var entity = this.CreateProxy(entityType, constructorArguments);

        config?.Invoke(entity);
        this.Add(entity);
        this.ChangeTracker.DetectChanges();
        return entity;
    }

    public void ApplyRelationships()
    {
        this.ChangeTracker.DetectChanges();
    }
}