In my project I have to parse JSON schema, that comes from server.
It has object "Properties", which in fact like Dictionary in curly braces. And, of course, JSONSerialization.jsonObject parses it as Dictionary.
Everything looks like OK, BUT: I use these Properties for building my view (it defines fields to be fiiled by user). Finally, I have to save order of these fields! But, as we know, immediately after the object is parsed to Dictionary, it looses keys order. Anybody knows how can I parse these object, saving fields order?
Additional information:
Structure of Properties is build by user in WEB, so their count is avsolutely random for mobile client. Furthermore, Every object in properties (e.g. Group) can have its own properties, containing other objects. So we have absolutely random tree of nested objects. And their order is necessary for us.
If you don't care about interoperability, meaning 3rd parties also being able to rely on order, you can try to find a parser that preserves order (such as by reading it into an OrderedMap in Python instead of a regular dict- obviously this will differ by language.)
If you care about 3rd parties, it's trickier. As the last person to respond noted, JSON itself does not support this, and JSON Schema is just JSON as far as parsing goes.
Related
I have a document (lets call it d1) that has multiple collections.
d1(FirestoreDocument) -> Collection1, Collection2, Collection3
These collections each have a unique name (in my case a date string with the format dd.MM.yy).
I need to retrieve all the documents that are that one collection. The problem is that I don't know how I can access a collection that I don't know the exact name of. Is there a function for firebase Firestore where you can for example call document.getAllCollections(completion...) and then get the documents for each collection individually?
There is a function for listing all collections called .listCollections() however it is a server-side function.
Meaning it's not available for client/mobile libraries
Since Swift is a mobile language it is not available there to my knowledge.
However, since you're formatting the subcollections as dd.MM.yy that means the subcollections are predictable (to a degree), so you could store a list of the subcollections a document has within it and then iterate over that list as a workaround, or iterate over a breadth of dates.
Another workaround would be to call listCollections server-side (assuming you have a server for your application written in Java, Python, Node.js, Go, PHP, C# or Ruby), and send that list of collections as a JSON array back to your client so it can iterate over it.
Is it possible to deserialize a subset of fields from a large object serialized using Apache Avro without deserializing all the fields? I'm using GenericDatumReader and the GenericRecord contains all the fields.
I'm pretty sure you can't do it using GenericDatumReader, but my question is whether it is possible given the binary format of Avro.
Conceptually, binary serialization of Avro data is in-order and depth-first. As you traverse the data, record fields are serialized one after the other, lists are serialized from the top to the bottom, etc.
Within one object, there no markers to separate fields, no tags to identify specific fields, and no index into the binary data to help quickly scan to specific fields.
Depending on your schema, you could write custom code to skip some kinds of data ... for example, if a field is a LIST of FIXED bytes, you could read the size of the list and just jump over the data to the next field. This is pretty specific and wouldn't work for most Avro types though (notably integers are variable length when encoded).
Even in that unlikely case, I don't believe there are any helpers in the Java SDK that would be useful.
In brief, Avro isn't designed to do that, and you're probably not going to find a satisfactory way to do a projection on your Schema without deserializing the entire object. If you have a collection, column-oriented persistence like Parquet is probably the right thing to do!
It is possible if the fields you want to read occur first in the record. We do this in some cases where we want to read only the header fields of an object, not the full data which follows.
You can create a "subset" schema containing just those first fields, and pass this to GenericDatumReader. Avro will deserialise those fields, and anything which comes after will be ignored, because the schema doesn't "know" about it.
But this won't work for the general case where you want to pick out fields from within the middle of a record.
There are at least 2 main collection types used in Realm:
List
Results
The relevant description from the documentation on a Results object says:
Results is an auto-updating container type in Realm returned from
object queries.
Because I want my UITableView to respond to any changes on the Realm Object Server, I really think I want my UITableView to be backed by a Results object. In fact, I think I would always want a Results object to back my UI for this reason. This is only reinforced by the description of a List object in the documentation:
List is the container type in Realm used to define to-many
relationships.
Sure seems like a List is focused on data modeling... So, being new to Realm and just reading the API, I'm thinking the answer is to use the Results object, but the tutorial (Step 5) uses the List object while the RealmExamples sample code uses Results.
What am I missing? Should I be using List objects to back my UITableViews? If so, what are the reasons?
Short answer: use a List if one already exists that closely matches what you want to display in your table view, otherwise use a Results.
If the data represented by a List that's already stored in your Realm corresponds to what you want to display in your table view, you should certainly use that to back it. Lists have an interesting property in that they are implicitly ordered, which can sometimes be helpful, like in the tutorial you linked to above, where a user can reorder tasks.
Results contain the results of a query in Realm. Running this query typically has a higher runtime overhead than accessing a List, by how much depends on the complexity of the query and the number of items in the Realm.
That being said, mutating a List has performance implications too since it's writing to the file in an atomic fashion. So if this is something that will be changing frequently, a Results is likely a better fit.
You should use Results<> as the Results is auto updating to back your UITableView. List can be used to link child models in a Realm model. where as Results is used to query the Realm Objects and you should add a Realm Notification Token so you know when the Results are updated and take necessary action (reload table view etc.) Look here for realm notifications: https://realm.io/docs/swift/latest/#notifications
P.S. The data in that example is just static and no changes are observed
I'm making a plist to hold genre synonyms. The list of synonyms for a given genre doesn't have any inherent order to it.
Should I use an array (which implies an order that doesn't exist) or a dictionary (which implies there's a corresponding value for each key, which doesn't exist).
Simply put--to store an unordered set in a plist, how should I represent it and why?
(To clarify: If there were a Set data structure in the plist editor, I would use that, but I only have Array and Dictionary to choose from.)
More details: I'm going to be looking up by the primary representation of the genre, thus the outer data structure in the plist has to be a dictionary.
But then for the synonyms, the only operation necessary is to enumerate them using a block.
So either an array or a dictionary will do. However, I'm concerned that using an array will imply an order that doesn't have any semantic meaning. On the other hand, is it a common occurrence to have dictionaries in plists that don't have a corresponding value?
Editing again to respond to Josh's comments:
I like your idea of converting into an NSSet after reading in the plist. However, I could still do that with a dictionary, right? So not sure why an array is the obvious choice.
If someone else edits the plist, they might think there's a meaning to the order, when in reality, the ordering is arbitrary.
Surprised no-one has defended using a dictionary instead of an array. Is there a reason a dictionary shouldn't be used in a plist for this purpose?
If you don't care about order, then the arbitrary order you get from building an array is equivalent to the arbitrary order you'd get by using a set. You can also very easily convert an array in a plist to an NSSet after reading it back: +[NSSet setWithArray:]
So use an array.
I would just use an array, since you say there's no corresponding key for a dictionary entry.
At the same time, if you're typing in a large number of entries into plist files (www), your fingers may get tired from dealing with the raw XML or plist editor stuff. You might want to consider a different way to save your synonyms?
Use an NSArray if lookup by item is not needed. If lookup is needed use an NSDictionary.
I'm attempting to submit a large database containing many tables to a web service by sending the data via JSON. Extracting the data and converting it to a JSON string is working fine but so far I have only implemented it to send one table at a time each with its own ASIHTTPRequest. My question is whether or not concatenating all the JSON strings generated from each table is a good idea or if I should first combine the tables in their abstract data form, before converting all of them together to JSON?
Alternatively if there is any other suggestion that would be good too.
It entirely depends on your needs. If the tables are unrelated, multiple requests may be more appropriate because if a request fails (timeouts or loss of connection), it won't affect any other requests. However if you have tables with associations with one another, it would be better to send it all in one go so either all the data transmitted wholly or did not so you don't end up with broken associations.
You can't just "concatenate" JSON strings. The result will not be legal JSON. You need to somehow "splice" them.
And, of course, the server on the other end must be capable of parsing the resulting JSON -- it may only expect one table at a time, eg.
I dont see any issue in doing any one of the two choices you proposed
But i would suggest concatenate the tables in the database before converting so that you dont deal with string concatenations and other form of processes