Re: [Zope-dev] ZPatterns, ZClasses, Specialists: Assigning responsibilities
At 05:13 PM 12/21/00 +1100, Itai Tavor wrote: I think you're right about this being an OrderLineItem. A couple of fine points, however... First, I don't think there needs to be an "OrderLineItemsWithGraphic" specialist, since there is nothing else that would talk to it. It's fine in this case to have the line item classes (either with graphic or without) handle their own UI snippets. UI delegation is for when an object needs to display UI for some *other* object than itself, since you can always use class extenders and other techniques to reshape the apparent class of an object retrieved from a specialist. The interface which other objects deal with is "OrderLineItem", and they simply expect a portion of the form to be rendered, and it's okay for the class to handle that. I got a bit confused here... the UI snippet for uploading a graphic actually comes from the Graphics Specialist. That's fine, but it should be by way of an object that's filling the OrderLineItem role, yes? Or I could eliminate the problem by uploading the graphic from a form displayed by the order line item after it has been added. That's actually what I thought you were doing/intending. Here's the question... how many behaviors are different in the order line item itself? Are you also using fulfillment line items? If the only difference to the order line item is that it references some additional data, then I'd say a single class would be fine. Most of the behavior probably comes in on the fulfillment line item, yes? Again, you can ask your FulfillmentLineItems specialist to create "newLineItemFor(orderLineItem)" and let it decide what kind of implementation to hand back. In this case, it probably will be a different class, while for the order line items, it may or may not buy you anything. I haven't thought of using fulfillment line items... not sure what they are for? An order is considered fulfilled once all items have been shipped, so order line items are responsible for tracking everything that happens until a ShipmentLineItem is created. The order line item for a customizable product tracks the product using state values like 'sent to factory', 'received from factory', etc. So it needs a new set of state values, as well as methods like 'sendManufacturingOrderToFactory'. What exactly does the fulfillment role you're referring to do? Does it do more than a shipment role? Fulfillment would be between ordering and shipping, covering such things as pulling items from the warehouse to customizing them with the graphic. I assumed that an order line item was only meaningful until you have a completed order. You may not need the complexity, but to me it seems like a seperate phase with a very different set of behaviors than what I would think of as an order line item. If I were doing an app like this, I'd at least have some sort of state/status objects to delegate these different behaviors to. But I'd say this could be left to the taste of the chef. :) P.S. By the way, I'm off on vacation later today, and won't be active on the list again for a little over a week. ___ Zope-Dev maillist - [EMAIL PROTECTED] http://lists.zope.org/mailman/listinfo/zope-dev ** No cross posts or HTML encoding! ** (Related lists - http://lists.zope.org/mailman/listinfo/zope-announce http://lists.zope.org/mailman/listinfo/zope )
Re: [Zope-dev] ZPatterns, ZClasses, Specialists: Assigning responsibilities
Phillip J. Eby wrote: This should probably be more like: product.addMeToOrder(): item = OrderLineItems.newLineItemFor(self) item.setQuantity(...) etc. order.addLineItem(item) customizable_product.addMeToOrder(): item = OrderLineItems.newLineItemFor(self) item.setGraphic(...) item.setQuantity(...) etc. order.addLineItem(item) This approach makes things more declarative. The product classes can have properties or interfaces that the OrderLineItems specialist can use to decide what kind of line item would serve them best. You can then change your line item assignment rules without necessarily requiring changes to the product classes. Yeah, it does work much better your way. And, getting OrderLineItems to decide on its own which type of object to add - haven't thought about doing it this way before. Thanks - something new to meditate on. I imagine, then, that the UI for uploading the graphic would be included in product.addMeToOrderForm, using a UI snippet from the OrderLineItemsWithGraphic Specialist. Then I could pass REQUEST on to order.addLineItem and to OrderLineItemsWithGraphic.add, which would then upload the file? I think you're right about this being an OrderLineItem. A couple of fine points, however... First, I don't think there needs to be an "OrderLineItemsWithGraphic" specialist, since there is nothing else that would talk to it. It's fine in this case to have the line item classes (either with graphic or without) handle their own UI snippets. UI delegation is for when an object needs to display UI for some *other* object than itself, since you can always use class extenders and other techniques to reshape the apparent class of an object retrieved from a specialist. The interface which other objects deal with is "OrderLineItem", and they simply expect a portion of the form to be rendered, and it's okay for the class to handle that. I got a bit confused here... the UI snippet for uploading a graphic actually comes from the Graphics Specialist. If I want to let the user upload the graphic as part of the product's addToOrderForm, Product needs to get this snippet - but Products and Graphics don't know about each other in the object model, so Product would have to ask OrderLineItems (not OrderLineItemsWithGraphic - I clearly don't need that) to get the snippet from Graphics for it, because it would violate Demeter if it talked directly to Graphics... Or I could eliminate the problem by uploading the graphic from a form displayed by the order line item after it has been added. Second, you need to define that interface so that the Order can give the line item constraints on how it does that UI, so it can share the screen and REQUEST with other objects/data that the Order needs. One easy way to do this is to use a namespace parameter, that simply gives the line item a name prefix to use on its fields. Alternatively, you can use the "record" approach, like this: INPUT TYPE="TEXT" NAME="lineitem1.desiredSize:record:int" VALUE="4" INPUT TYPE="FILE" NAME="lineitem1.imageFile:record:file" ... The resulting REQUEST object from submitting the form will contain a single object, "lineitem1", with "desiredSize" and "imageFile" attributes, so you'll only have to pass a single parameter back to the line item. I've never tried doing a record with a file in it before, so I don't really know how well that works. I've been solving the REQUEST sharing problem using a prefix on form fields... but I like the "record" idea - it makes it much easier to pass the form data around... I'll try it with a file soon. I imagine it would work fine. Woof... so long. I'd appreciate any comments on this - especially on the question on whether it's better to have a specialized type of OrderLineItem, or to link the standard OrderLineItem to a Product object in case of a standard product, or, in the case of a customizable product, to a new object which stores the graphic and tracks the fabrication of the customized item. Here's the question... how many behaviors are different in the order line item itself? Are you also using fulfillment line items? If the only difference to the order line item is that it references some additional data, then I'd say a single class would be fine. Most of the behavior probably comes in on the fulfillment line item, yes? Again, you can ask your FulfillmentLineItems specialist to create "newLineItemFor(orderLineItem)" and let it decide what kind of implementation to hand back. In this case, it probably will be a different class, while for the order line items, it may or may not buy you anything. I haven't thought of using fulfillment line items... not sure what they are for? An order is considered fulfilled once all items have been shipped, so order line items are responsible for tracking everything that happens until a ShipmentLineItem is created. The order line item for a
Re: [Zope-dev] ZPatterns, ZClasses, Specialists: Assigning responsibilities
At 04:21 PM 12/18/00 +1100, Itai Tavor wrote: This is how I see it: - Products Specialist productRack customizableProductRack - OrderLineItem Specialist lineItemRack lineItemWithGraphicRack - product.addMeToOrder(): order.addLineItem(product_id=id, add='lineItem') - custimazable_product.addMeToOrder(): order.addLineItem(product_id=id, add='lineItemWithGraphic') This should probably be more like: product.addMeToOrder(): item = OrderLineItems.newLineItemFor(self) item.setQuantity(...) etc. order.addLineItem(item) customizable_product.addMeToOrder(): item = OrderLineItems.newLineItemFor(self) item.setGraphic(...) item.setQuantity(...) etc. order.addLineItem(item) This approach makes things more declarative. The product classes can have properties or interfaces that the OrderLineItems specialist can use to decide what kind of line item would serve them best. You can then change your line item assignment rules without necessarily requiring changes to the product classes. I imagine, then, that the UI for uploading the graphic would be included in product.addMeToOrderForm, using a UI snippet from the OrderLineItemsWithGraphic Specialist. Then I could pass REQUEST on to order.addLineItem and to OrderLineItemsWithGraphic.add, which would then upload the file? I think you're right about this being an OrderLineItem. A couple of fine points, however... First, I don't think there needs to be an "OrderLineItemsWithGraphic" specialist, since there is nothing else that would talk to it. It's fine in this case to have the line item classes (either with graphic or without) handle their own UI snippets. UI delegation is for when an object needs to display UI for some *other* object than itself, since you can always use class extenders and other techniques to reshape the apparent class of an object retrieved from a specialist. The interface which other objects deal with is "OrderLineItem", and they simply expect a portion of the form to be rendered, and it's okay for the class to handle that. Second, you need to define that interface so that the Order can give the line item constraints on how it does that UI, so it can share the screen and REQUEST with other objects/data that the Order needs. One easy way to do this is to use a namespace parameter, that simply gives the line item a name prefix to use on its fields. Alternatively, you can use the "record" approach, like this: INPUT TYPE="TEXT" NAME="lineitem1.desiredSize:record:int" VALUE="4" INPUT TYPE="FILE" NAME="lineitem1.imageFile:record:file" ... The resulting REQUEST object from submitting the form will contain a single object, "lineitem1", with "desiredSize" and "imageFile" attributes, so you'll only have to pass a single parameter back to the line item. I've never tried doing a record with a file in it before, so I don't really know how well that works. Woof... so long. I'd appreciate any comments on this - especially on the question on whether it's better to have a specialized type of OrderLineItem, or to link the standard OrderLineItem to a Product object in case of a standard product, or, in the case of a customizable product, to a new object which stores the graphic and tracks the fabrication of the customized item. Here's the question... how many behaviors are different in the order line item itself? Are you also using fulfillment line items? If the only difference to the order line item is that it references some additional data, then I'd say a single class would be fine. Most of the behavior probably comes in on the fulfillment line item, yes? Again, you can ask your FulfillmentLineItems specialist to create "newLineItemFor(orderLineItem)" and let it decide what kind of implementation to hand back. In this case, it probably will be a different class, while for the order line items, it may or may not buy you anything. Anyway... remember that Specialists are there to hide implementation decisions like what classes are being used. If you look at the ZPatterns Wiki you'll see references to some of the design patterns which Specialists are an instance of, which will give you some hints as to the many kinds of things they can "hide" for you (and which therefore you should avoid revealing in other code). One of those patterns is that as an object "trader" or "broker", Specialists can be used to create new instances of objects that meet a certain interface, but whose implementation has been selected on the basis of declarative criteria by the requesters. ___ Zope-Dev maillist - [EMAIL PROTECTED] http://lists.zope.org/mailman/listinfo/zope-dev ** No cross posts or HTML encoding! ** (Related lists - http://lists.zope.org/mailman/listinfo/zope-announce http://lists.zope.org/mailman/listinfo/zope )
Re: [Zope-dev] ZPatterns, ZClasses, Specialists: Assigning responsibilities
Itai Tavor wrote: I have the following ZClasses, with matching Specialists: Product, Graphic, Order, OrderLineItem. When a customer adds a product to their order, they have to provide a graphic file which will be printed on the product (imagine buying a lunch box with your cat's photo on it). The Graphics Specialist can provide a addGraphicSnippet form. But who's responsible for asking for this graphic when adding the product to the order? Is it still the Product object? But a Product turns into a Product-with-Graphic only when it's a part of an order, so is it correct for the Product to even know about Graphics? the alternative is to move the addToOrder methods to either Order or OrderLineItems, but this doesn't make any more sense because these would then have to know a lot more about a Product than is good for them. Any ideas? Sounds to me like you have a new type of Product. You have your basic products (of which there are many kinds), and you have ProductWithGraphic products. A ProductWithGraphic is a "calculated product": it is composed of a basic product and a graphic. Its cost, delivery time, packing charge, and so forth, are calculated based on the combination of the basic product and the graphic. To the rest of the application, a ProductWithGraphic is just another kind of product. -- Steve Alexander Software Engineer Cat-Box limited http://www.cat-box.net ___ Zope-Dev maillist - [EMAIL PROTECTED] http://lists.zope.org/mailman/listinfo/zope-dev ** No cross posts or HTML encoding! ** (Related lists - http://lists.zope.org/mailman/listinfo/zope-announce http://lists.zope.org/mailman/listinfo/zope )
