I"m working with a core data model of Employees. Each employee is assigned a building and a department. I am returning everyone in building 1 with the predicate, building == 1 and using the sectionNameKeyPath parameter to break the result set down into groups by department.
Right now I have a sort descriptor ordering the departments alphabetically, but is there a way to ignore sorting them alphabetically and organize them in my own way, like engineers first, security second so on and so forth? I'm still getting used to the terminology and there's probably something I'm overlooking.
Thanks,
Note that the sortDescriptors property of the fetched results controller is an array, so you can set multiple sort descriptors which will be used in the order you specify them (e.g. first by department.name, then by lastName, then by firstName).
Related
I have two collections
Customers
Products
I have a field called "orders" in each of my customer document and what this "orders" field does is that it stores a reference to the product Id which was ordered by a customer, now my question is since I'm referencing product Id and if I update the "title" of that product then it will also update in the customer's order history since I can't embed each order information since a customer may order thousands of products and it can hit 16mb mark in no time so what's the fix for this. Thanks.
Create an Orders Collection
Store ID of the user who made the order
Store ID of the product bought
I understand you are looking up the value of the product from the customer entity. You will always get the latest price if you are not storing the order/price historical transactions. Because your data model is designed this way to retrieve the latest price information.
My suggestion.
Orders place with product and price always need to be stored in history entity or like order lines and not allow any process to change it so that when you look up products that customers brought you can always get the historical price and price change of the product should not affect the previous order. Two options.
Store the order history in the current collection customers (or top say 50 order lines if you don't need all of history(write additional logic to handle this)
if "option1" is not feasible due to large no. of orders think of creating an order lines transaction table and refer order line for the product brought via DBref or lookup command.
Note: it would have helped if you have given no. of transactions in each collection currently and its expected rate of growth of documents in the collection QoQ.
You have orders and products. Orders are referencing products. Your problem is that the products get updated and now your orders reference the new product. The easiest way to combat this issue is to store full data in each order. Store all the key product-related information.
The advantage is that this kind of solution is extremely easy to visualize and implement. The disadvantage is that you have a lot of repetitive data since most of your products probably don't get updated.
If you store a product update history based on timestamps, then you could solve your problem. Products are identified now by 3 fields. The product ID, active start date and active end date. Or you could configure products in this way: product ID = product ID + "Version X" and store this version against each order.
If you use dates, then you will query for the product and find the product version that was active during the time period that the order occurred. If you use versions against the product, then you will simply query the database for the particular version of the product itself. I haven't used mongoDb so I'm not sure how you would achieve this in mongoDb exactly. Naively however, you can modify the product ID to include the version as well using # as a delimiter possibly.
The advantage of this solution is that you don't store too much of extra data. Considering that products won't be updated too often, I feel like this is the ideal solution to your problem
I'm trying to figure out how to query with filter with Geofire.
Suppose I have restaurants with different category. and I want to add that category to my query. How do I go about this?
One way I have now is querying the key with Geofire, run the for loop through each key and get the restaurant, and insert the appropriate restaurant to the array.
These seems so inefficient. Is there any other way to go about this?
Ideally I will have the filtered results, and only load each item when they're about to be shown.
Cheers!
Firebase queries can only filter by one condition. Geofire already does quite some "magic" to allow it to filter on both longitude and latitude. Adding another property to that equation might be possible, but is well beyond what Geofire handles by default. See GeoFire: How to add extra conditions within the query?
If you only ever want to access one category at a time, you can put the restaurants in a top-level node per category and point Geofire to one category.
/category1
item1
g: "pns0h0mf2u"
l: [-53.435719, 140.808716]
item2
g: "u417k3dwub"
l: [56.83069, 1.94822]
/category2
item3
g: "8m3rz3s480"
l: [30.902225, -166.66809]
/items
item1: ...
item2: ...
item3: ...
In the above example, we have two categories: category1 with 2 items and category2 with just 1 item. For each item, we see the data that Geofire uses: a geohash and the longitude and latitude. We also keep a single list with the other properties of these 3 items.
But more commonly, you simply do the extra filtering in client-side code. If you're worried about the performance of that: measure it, share the code, JSON data and measurements.
This is an old question, but I've seen it in a few places on the web, so I thought I might share one trick I've used.
The Problem
If you have a large collection in your database, maybe containing hundreds of thousands of keys, for example, it might not be feasible to grab them all. If you're trying to filter results based on location in addition to other criteria, you're stuck with something like:
Execute the location query
Loop through each returned geofire key and grab the corresponding data in the database
Check each returned piece of data to see if it matches the other criteria
Unfortunately, that's a lot of network requests, which is quite slow.
More concretely, let's say we want to get all users within e.g. 100 miles of a particular location that are male and between ages 20 and 25. If there are 10,000 users within 100 miles, that means 10,000 network requests to grab the user data and compare their gender and age.
The Workaround:
You can store the data you need for your comparisons in the geofire key itself, separated by a delimiter. Then, you can just split the keys returned by the geofire query to get access to the data. You still have to filter through them, but it's much faster than sending hundreds or thousands of requests.
For instance, you could use the format:
UserID*gender*age, which might look something like facebook:1234567*male*24. The important points are
Separate data points by a delimiter
Use a valid character for the delimiter -- "It can include any unicode characters except for . $ # [ ] / and ASCII control characters 0-31 and 127.)"
Use a character that is not going to be found elsewhere in your database - I used *, but that might not work for you. Do not use any characters from -0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ_abcdefghijklmnopqrstuvwxyz, since those are fair-game for keys generated by firebase's push()
Choose a consistent order for the data - in this case, UserID first, then gender, then age.
You can store up to 768 bytes of data in firebase keys, which goes a long way.
Hope this helps!
I have a situation where i need to sort the data using multiple sort descriptors. I want to sort the data initially with two components which are numbers in descending order. Then I should show the data on the table view sorted with name component and use the sectionNameKeyPath to get the sections.
I want the data should be sorted out first with the two specified components and then the result with name. Is this possible using NSfetchedResultsController. I am using this fetchedresultscontroller in data source for tableview. Is there anyway to re sort the fetchedresultscontroller?
I can sort it by taking an array and using sortdescriptor on that, but I want fetchedresultscontroller to show the section details and etc.
Is there any way?
I don't really sure if I have understood your answer.
But there is a property called sortDescriptors in NSFetchRequest which you may use it to sort.
And it's an array so you can supply multi NSSortDescriptor objects
And if you want to resort it.
I know two ways:
Store the result in an array like you said and resort it.
Change the sortDescriptors and re performFetch of the FRC
I have a CoreData entity called Item with two values (well, two values relevant to this question).
Item
---------------
id - NSString
name - NSString
Every item has a unique ID and SHOULD have a unique name.
(BTW, the id is not used for CoreData it is used for communicating with the server).
There are a couple of items which appear to have duplicate names and I'm trying to find a query that returns all items that have an item in the table with a duplicate name.
Is this possible?
If so, can someone provide an NSPredicate (or method) to do this.
I do not think that it is possible to fetch exactly the items with duplicate names with a Core Data fetch request. (I think there was a similar question some time ago here on SO, but I cannot find it right now.)
You could fetch all items sorted by the name attribute. Then the duplicates can be found with a single loop over the result array.
I'm using search logic to filter and order my results but it removes records from my results when I order by a association and when that association is not always present for all records.
For example say I have a user model which can have one vehicle model but does not have to, if I have a results table where you can order by the users vehicles make I would hope all users without a vehicle record would be considered empty strings and therefore ordered all at the beginning followed by the other user records which have vehicles ordered by the make name.
Unfortunately all the user records which do not have a vehicle are removed from the results.
Is there anyway round this and still use search logic as I find it extremely useful
I think you'll have to explicitly assign a default vehicle that has an empty name