Is there any possibility to get information about change in listings from Amazon. Like I would like to get the listings which are changed on amazon.
There may be an ever better option for what you are asking. MWS has the Subscriptions API which will send you a notification when certain things about an item change rather than having to query the items and log differences yourself.
You can get notifications on things such as:
AnyOfferChanged - When any of the top 20 offers (prices) on the item changes
FulfillmentOrderStatus - This one is interesting as you can get notificaitons on fulfillment of the item (i.e. when item comes back in stock, when it is on the way, when a shipper has a planned order, etc)
FeePromotion - When an item gets a promotional price (lightning deal, etc)
Related
I am building a simple Chat App using Firebase and Ionic. I am trying to keep track of number of messages that are unread for different groups that the user is member of (like WhatsApp).
I have the messages linked to $scope through $firebaseArray
$scope.messages = $firebaseArray(<ref to message path in firebase>);
$scope.messages is iterated over and shown in the view. When a new message arrives it automatically shows up in the group being viewed. I want to keep track of messages not viewed. I am not quite sure of the best way to keep track of which messages the user has seen. I see suggestions here to keep track of timestamp when a user last visited a group but am wondering if there is a better/simpler solution to this.
The things that come to mind that I need to do are -
Setup some sort of monitoring for all groups the user is member of not just the one being viewed by the user. If user is member of 50 groups I need to monitor all 50 of them individually (wonder what, if any, performance implications that has). Here I will need to setup a child_added monitoring for each of the groups the user is member of
Track timestamp for last time a user was in a group
As the user switches groups, change the $firebaseArray to monitor the new group and cancel the $firebaseArray setup for the previous. Change the child_added monitoring for the new group to the group being viewed previously
If the user moves to another part of the app where he is not looking at any group messages (perhaps in a setting section) then again be aware of that and monitor all groups - remove the firebeaseArray from the group last being viewed and add a child_added monitoring when user moves away
If the user goes to another application and pushes the Chat application in the background then I am a little unsure of what to do
How does the code determine that the group whose messages the user was looking at is no longer active and new messages coming in now need to be counted
I am assuming I need to monitor for the App Pause and Resume events to address that. Is there a better way?
Trying to keep my code simple but feels like monitoring for unread messages is a significant chunk of work. Thanks for any ideas or pointers to sample code or to simplify this.
-S
Many examples on the net show you how to use ng-repeat with in-memory data, but in my case I have long table with infinite scroll that gets data by sending requests to a REST API (scroll down - fetch some data, scroll down again - fetch some more data, etc.). It does work, but I'm wondering how can I integrate that with filters?
Right now I have to call a specific method of API service that makes a request based on text in "search" input box and then controller updates $scope.data.
Is it possible to build a custom filter that would do that? And then my view would be utterly decoupled from the service and I could declaratively tell it how to group and order and filter data, regardless if it's in-memory or comes from a remote server, server that can serve only limited records at a time.
Also later I'm gonna need grouping and ordering as well, I'm so tempted to download the entire dataset and lock parts of the app responsible for grouping, searching and ordering (until all data is on the client), but:
a) that dataset is huge (hundred thousands of records)
b) nobody wants to deal with cache invalidation headaches
c) doing so feels so damn wrong, you don't really expect me to 'keep' all that data in-memory, right?
Can you guys point me to maybe some open-source examples where I can steal some ideas from?
Basically I need to build a service and filters that let me to work with my "pageable" data that comes from api, like it's in memory-data.
Regardless of how you choose to solve it (there are many ways to infinite-scroll with angular, here is one: http://binarymuse.github.io/ngInfiniteScroll/), at its latest current beta version, ng-repeat works really bad with large amount of data - so do filters. The reason is obvious - pulling so much information for changes is a tuff job. Moreover, ng-repeat by default will re-draw your complete list every time something changes.
There are many solutions you can explore in this area, here are the ones I found productive:
http://kamilkp.github.io/angular-vs-repeat/#?tab=8
http://www.williambrownstreet.net/blog/2013/07/angularjs-my-solution-to-the-ng-repeat-performance-problem/
https://github.com/allaud/quick-ng-repeat
You should also consider the following, which really helps with large amounts of data.
https://github.com/Pasvaz/bindonce
Updated
I guess you can't really control your server output, because filtering and ordering large amount of data are better off done on the server side.
I was pointing out the links above since even if you write your own filters (and order-bys), which is quite simple to do - http://jsfiddle.net/gdefpfqL/ - (filter by some company name and then click the "Add More" button - to add more items). ordering by is virtually impossible if you can't control the data coming for the server - the only option is getting it all, ordering and then lazy load from the client's memory. So if each of your list items doesn't have many binding by it self (as in the example I've added) - the list item is a fairly simple one (for instance: you simply present the results as a plain text in a <li>{{item.name}}</li> then angular ng-repeat might work for you. In this case, filters will work as expected - say you filter by searched text:
<li ng-repeat="item in items | filter:searchedText"></li>
even for new items added after the user has searched a text, it will still works because the magic of binding.
As the subject reads, I have several use cases where it would be really useful to change the values in a picklist to only include certain values when data in another object changes, is this possible to do from within a trigger?
e.g. Update a picklist of active employees when people leave or join the company.
Out of the box - no.
Picklists can be controlled with Metadata API (and in future maybe Tooling API too) - but from Apex point of view you need a callout. Either to external system that'll leverage the Metadata API or have a look at Adding Columns dynamically to Salesforce Reports - there's an interesting "mdapi" plugin that you might decide to use. Bear in mind destructive changes (like removal of values) are pretty annoying to execute...
In this particular example it's very tempting to say "you're doing it wrong" :(
A lookup to User will out of the box hide users that aren't active. Problem solved.
What are you going to do when the organisation will grow (through acquisitions?) and you'll hit the limit of max 1000 picklist values? http://help.salesforce.com/apex/HTViewHelpDoc?id=picklist_limitations.htm (probably even sooner depending how much of the 15K limit you've used already)
Personally I consider a picklist with anything more than 50 entries a crappy UI / user experience. Well, unless there's some kind of autocomplete paired with it. Scroll, scroll, scroll...
I have WCF server and silverlight client. The client call the server to get list of items.
There is some cases that the item list is very big and I want to have the ability to get the items in more then one call -
Call1 => get the items 0-100
Call2 ( if the user click on 'more' button ) => get the item 101-200
.
.
Call N => get the 100*n - 100*(n+1) items.
How can I do it ?
Is there some 'easy' pattern to do it ?
Thanks.
If you have a standard page size of 100 then have the client pass the page they want to the service. Or get the client to tell the service how big their pages are and which page they want
You could hold in memory on the service which page the client has and then have then say "Next" but holding in-memory state in the service on behalf of the client reduces scalability and increases fragility (if that state is lost then the client has to start paging again.
making the client explicitly say what they want is a more robust and scalable solution and has an easy LINQ implementation with Skip and Take
As Richard mentions, paging is a common option. Also, returning the results as a stream (and not a buffered byte[] array but an actual stream -- WCF has some caveats around use of stream) is going to generally be most efficient. Also as marc_s noted, Silverlight local storage isn't huge, so keep that handicap in mind.
The chance of a user 'consuming' more than 100 items in one go is very small, even if the items have very little detail, maybe add navigation (categories etc) as filters to the data so the user will only get the 20 or so items they are actually interested in. Tree views can be quite handy to break lists up into smaller lists that are more relevant to users, but there are many ways of doing this...
Lets take an example of WinForms applcation and making invoice. On the Invoice form we retrieve a list of products, so the user will be ale to pick products for current invoice. Lets also consider that during this process user realizes that he needs to add a new product (or edit current) to ProductList before he can place it in invoice. So he opens a ProductForm where all the products are retreived (again).
It could also be in opposite order, that user first edits Products, and then without closing the Products Form, opens new Invoice. The principle is that data is two times loaded, and effectively its the same data.
What is the propper way to handle this scenario, so we can tell one form that data is already loaded, and to retrieve that data from memory? And when all the consumers (Forms) of the data are closed, then also the data should be released from memory? Or I am going in wrong direction, and there is a better way?
Thanks,
Goran
Definitelly go with data loaded "twice" or you will introduce much worse problems.
Sharing data means sharing ObjectContext. Even in WinForms application this is considered as bad approach. Check this article (it is about NHibernate but the description is valid for EF as well).
The problem is that ObjectContext is unit of work. If share context between two windows you can easily get into situation where you modify data in first window (without saving them!) and you continue in second window where you push save button but it will save data from both windows! You can't selectively save data only from one window when you share the context.
If the Controls that are using the data are all child controls of a shared Parent control, then you could just pass around the datacontext, so that they all shared the same datacontext.
However, the general use case with databases, which is what backs EF in most cases, is to read the data in each time that it is needed.
A solution to this if as you say you already have the item being used in one form is to just take a Refrence to that item into your new form.
So in the case Where you have an invoice which has a Product List and you want to add to the product list, you could pass the product list from the invoice to the opening product list.
There are some issues with this:
If another user changes the datasource while one has opened it (a.k.a. Concurrency)
Handling save don't save scenarios where they may have made a change in one area that they don't actually want added to the data.
However, unless it is a true performance issues, I would just load the data every time. You can simplify this a lot by using the repository pattern, so you can just call a single method to get a list of products or an invoice, or whatever part of data you need.