C#•9mo ago

❔ EFCore Expression Reuse Translations`

I have the following piece of projector:

public static Expression<Func<Order, OrderModel>> ProjectToOrderModel()
    {
        return order => new OrderModel
        {
            Uid = order.Uid,
            Table = ProjectToOrderTable(order.Table),
        };
    }

    public static TableModel ProjectToOrderTableModel(Table table) => new()
    {
        Id = table.Id,
        Name = table.Name
    };

public static Expression<Func<Order, OrderModel>> ProjectToOrderModel()
    {
        return order => new OrderModel
        {
            Uid = order.Uid,
            Table = ProjectToOrderTable(order.Table),
        };
    }

    public static TableModel ProjectToOrderTableModel(Table table) => new()
    {
        Id = table.Id,
        Name = table.Name
    };

Where Order is the EFCore entity and OrderModel is a POCO. Whenever I do the following : db.Orders.Select(Mapper.ProjectToOrderModel()) The correct SQL is generated by using the projection fields and not querying the whole columns. This surprised me because ProjectToOrderTableModel is a function and not an expression. However things get confusing when we get into lists. Rewriting the above snippet trying to include a nested collection

public static Expression<Func<Order, OrderModel>> ProjectToOrderModel()
    {
        return order => new OrderModel
        {
            Uid = order.Uid,
            Table = ProjectToOrderTable(order.Table),
            Items = order.OrderItems.AsQueryable().Select(MapToOrderItemsModel).ToList(),
        };
    }

    public static TableModel ProjectToOrderTableModel(Table table) => new()
    {
        Id = table.Id,
        Name = table.Name
    };

    public static OrderItemModel MapToOrderItemsModel(OrderItem i)
    {
         return new()
            {
                Uid = i.Uid,
                Name = i.Title,
                Price = i.Price
            };
    }

public static Expression<Func<Order, OrderModel>> ProjectToOrderModel()
    {
        return order => new OrderModel
        {
            Uid = order.Uid,
            Table = ProjectToOrderTable(order.Table),
            Items = order.OrderItems.AsQueryable().Select(MapToOrderItemsModel).ToList(),
        };
    }

    public static TableModel ProjectToOrderTableModel(Table table) => new()
    {
        Id = table.Id,
        Name = table.Name
    };

    public static OrderItemModel MapToOrderItemsModel(OrderItem i)
    {
         return new()
            {
                Uid = i.Uid,
                Name = i.Title,
                Price = i.Price
            };
    }

This fails because the Expression of type System.Func cannot be translated, which makes sense. I cannot understand how it works for a singular model, but it cannot work on a collection... ? Is there any tracking bug, or is it a forbidden thing to do?! P.S: I'm aware of the solution of implementing a public static Expression<Func<OrderItem, OrderItemModel>>, I just don't understand why the above doesn't work

9 Replies

Angius•9mo ago

The above doesn't work, because it's a Func not an Expression

UltraWelfare•9mo ago

My question was why a function worked in the table but not inside the list turns out, the function is called on the table, but in the select statement is just registered

UltraWelfare•9mo ago

https://stackoverflow.com/questions/77279017/efcore-7-reusable-expression-translation-issues-on-collections

Stack Overflow

EFCore 7 reusable expression translation issues on collections

I have the following piece of projector: public static Expression<Func<Order, OrderModel>> ProjectToOrderModel() { return order => new OrderModel { Ui...

UltraWelfare•9mo ago

I'm a bit worried about this particular comment https://stackoverflow.com/questions/77279017/efcore-7-reusable-expression-translation-issues-on-collections#comment136239711_77279017 If anyone has any recommendations, I'll happily hear

Angius•9mo ago

Idk, I just use expressions, haven't used automapper in a while

UltraWelfare•9mo ago

Yeah I've used it and I don't like the profiles the dependency injection you have to do + the reflection that it does in the background I'd rather just handwrite them.. Especially when the field names are not 1-1... In that case I'd write more code and still end up manually mapping the fields lol

Angius•9mo ago

You can at least shorten your

public static Expression<Func<Order, OrderModel>> ProjectToOrderModel()
    {
        return order => new OrderModel
        {
            Uid = order.Uid,
            Table = ProjectToOrderTable(order.Table),
            Items = order.OrderItems.AsQueryable().Select(MapToOrderItemsModel).ToList(),
        };
    }

public static Expression<Func<Order, OrderModel>> ProjectToOrderModel()
    {
        return order => new OrderModel
        {
            Uid = order.Uid,
            Table = ProjectToOrderTable(order.Table),
            Items = order.OrderItems.AsQueryable().Select(MapToOrderItemsModel).ToList(),
        };
    }

public static Expression<Func<Order, OrderModel>> ProjectToOrderModel = (order) => new OrderModel
        {
            Uid = order.Uid,
            Table = ProjectToOrderTable(order.Table),
            Items = order.OrderItems.AsQueryable().Select(MapToOrderItemsModel).ToList(),
        };

public static Expression<Func<Order, OrderModel>> ProjectToOrderModel = (order) => new OrderModel
        {
            Uid = order.Uid,
            Table = ProjectToOrderTable(order.Table),
            Items = order.OrderItems.AsQueryable().Select(MapToOrderItemsModel).ToList(),
        };

UltraWelfare•9mo ago

Actually in the snippet I posted in stackoverflow, I made it a property with only a { get; } But I totally understand what you mean

Accord•9mo 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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❔ EFCore Expression Reuse Translations`