What is the correct way to read the content of a document as value without subscription ?
Keep in mind that when persistence is enabled the Observer receives two values, first value is the locally persisted one and the second is the actual value that is stored in the database.
You can use get() method to retrieve the contents of a single document.
For More details you can check this StackOverflow thread
Related
I am trying to create some firestore security rules. However, every rule that I write that involves something other than the users database pulling the document of the current user results in an error. There is some difference I am missing.
Here is the query and the data. The resource object is always null. Any get function that involves pulling from the design database using the designId variable also results in null.
You're putting a pattern into the form, which is not valid. You need to provide the specific document that you want to simulate a read or write. This means you need to copy the ID of the document into that field. It should be something like "/designs/j8R...Lkh", except you provide the actual value.
I'm new to dart/flutter and am building an app right now that keeps track of some data on each user in a firstore database. I have a 'Users' collection which contains a document for each user, and one of the fields in the user document is the "UID" received through firebase_auth.
That being said, to make sure I have access to the latest copy of a user document, I hold a Stream. I want to somehow access the "UID" field from the latest snapshot in the stream and then do some other operations with it.
Is there anyway to do this? Am I using/understanding streams incorrectly?
If you only ever need the UID to build other widgets, you can simply use a StreamBuilder which will rebuild its children whenever a new value is emitted from the stream (which you get a copy of). However, if you need to access the latest UID at some arbitrary point of time, check out RxDart's BehaviorSubject which provides constant-time synchronous access to the latest emitted value, if one exists. It is very helpful for handling state in general.
I am trying to paginate data with Firestore, and would be ordering data on columns where duplicates are expected, if the pagination happens to be among those values its expected that it won't work correctly.
I can work around this issue by using StartAfter based on Document ID which will be always be unique.
One way I can accomplish this is passing id of the last document to server side rest api request. This would require two steps, i.e. to fetch the DocumentSnapshot using the DocumentId and constructing the query based on it
var lastSnapshot = fetchSnapshot(id);
citiesRef.OrderBy("Population").StartAfter(lastSnapshot);
Other approach is to persist the DocumentId in the document while creation.This would require two steps each time when the document is created, one to create and the other to update immediately with Id generated (As I don't see a way to persist DocumentId during creation itself)
citiesRef.OrderBy("Population").StartAfter(lastId);
Which one of these is a good approach to follow, either to fetch DocumentSnapshot and not to persist id into the document, or perform two operations by persisting the DocumentId in the first place and using it as key for StartAfter.
Decided to go with Option 1, instead of persisting Document ID in the Document itself as in Option 2.
Apple Documents says "If a context already contains a managed object for an object returned from a fetch, then the existing managed object is returned in the fetch results"
My Question is If I have updatd the object in the context but not saved the context yet then what object will Fetch Request return? Updated object from Context or New one from Datastore.
Your quote answers that question; it will be the one in memory. With that comes the caveat that if you make a new NSManagedObjectContext and perform the fetch request on that context, you will get the object from the data store.
It depends on the includesPendingChanges setting of the fetch request. By default,
includesPendingChanges is YES, which means that the fetch will get currently unsaved
changes.
However, if you use the NSDictionaryResultType result type for the fetch request,
this implicitly implies includesPendingChanges = NO, and you will get only results
from the store.
I guess it returns Updated object from Context.
Note: Due to low reputation i have to put as answer.
The extjs Jsonstore class has a method commitchanges().
Now considering that the javascript code will send an AJAX request to a servlet and not to a db directly, what do we need a commitchanges() method?
Whenever user changes anything in the form panel's or UI components that data is changed in record, but at this time record will maintain a list of modified properties in the record and store maintains a list of modified records in the store
So whenever you send a request to save the data to server, after successful save you will get back a success response, on this response store need to make sure that the saved record will be removed from the list of records that are modified in the store and also remove list of modifications from the record instance to indicate that save operation was successful
So the operations of removing list of modified properties from record instance is performed by record.commit method and operations of removing saved record from list of modified records from store is performed by store.commitChanges method which in turn will call record.commit for every record which is saved correctly on server