Reddit EF Repository pattern stuff

wat.cs

public static class WatCache<T> where T : class
{
    private static ConcurrentDictionary<object, Action<T,Guid>> _cache = new();

    public static Action<T, Guid> Get(Expression<Func<T, object>> selector) => _cache.GetOrAdd(selector, sel =>
    {
        var expr = (Expression<Func<T, object>>)sel;
        var member = expr.Body as MemberExpression;
        var prop = member!.Member as PropertyInfo;
        var ep = Expression.Parameter(typeof(T), "entity");
        var gp = Expression.Parameter(typeof(Guid), "id");
        var assignExp = Expression.Assign(Expression.Property(ep, prop!), gp);
        var lambda = Expression.Lambda<Action<T, Guid>>(assignExp, ep, gp);
        return lambda.Compile();
        
    });
}
public static class Wat
{
    public static async Task AddCollectionEntry<TCollectionType>(this DbContext _context, Guid parentId, Expression<Func<TCollectionType, object>> parentProperty, TCollectionType subEntity) where TCollectionType : class
    {
        WatCache<TCollectionType>.Get(parentProperty)(subEntity, parentId);

        _context.Set<TCollectionType>().Add(subEntity);
        await _context.SaveChangesAsync();
    }
}

wat2.cs

public static class WatCache<T> where T : class
{
    private static ConcurrentDictionary<object, Action<T,Guid>> _cache = new();

    private static Action<T,Guid> BuildArg<TGuid>(object mainObject)
    {
        var useConvert = (typeof(TGuid) == typeof(Guid?));
        var expr = (Expression<Func<T, TGuid>>)mainObject;
        var member = expr.Body as MemberExpression;
        var prop = member!.Member as PropertyInfo;
        var ep = Expression.Parameter(typeof(T), "entity");
        var gp = Expression.Parameter(typeof(Guid), "id");
        var assignExp = Expression.Assign(Expression.Property(ep, prop!),
            useConvert ? Expression.Convert(gp, typeof(Guid?)) : gp);
        var lambda = Expression.Lambda<Action<T, Guid>>(assignExp, ep, gp);
        return lambda.Compile();
    }

    public static Action<T, Guid> Get(Expression<Func<T, Guid>> selector) => 
        _cache.GetOrAdd(selector,
            static s=> BuildArg<Guid>(s));

    public static Action<T, Guid> Get(Expression<Func<T, Guid?>> selector) =>
        _cache.GetOrAdd(selector, 
            static s=> BuildArg<Guid?>(s));
}
public static class Wat
{
    public static async Task AddCollectionEntry<TCollectionType>(this DbContext _context, Guid parentId, Expression<Func<TCollectionType, Guid>> parentProperty, TCollectionType subEntity) where TCollectionType : class
    {
        WatCache<TCollectionType>.Get(parentProperty)(subEntity, parentId);

        _context.Set<TCollectionType>().Add(subEntity);
        await _context.SaveChangesAsync();
    }
    
    public static async Task AddCollectionEntry<TCollectionType>(this DbContext _context, Guid parentId, Expression<Func<TCollectionType, Guid?>> parentProperty, TCollectionType subEntity) where TCollectionType : class
    {
        WatCache<TCollectionType>.Get(parentProperty)(subEntity, parentId);

        _context.Set<TCollectionType>().Add(subEntity);
        await _context.SaveChangesAsync();
    }
}