So I'm using firebase cloud firestore with swift (but this is a general question with firestore), and I want to sort through some documents using a query, something like
fetchQ.whereField(fieldName, isGreaterThan: startingValue)
But then I want to guarantee some kind of order if the field has the same value, and it stands to reason that the document id is good for this, so I add
.order(by: FieldPath.documentID(), descending: false)
But now I get the error in the console where I have to paste the url in order to create a composite index. I do that, except it's only for the single index "fieldName", leaving out the document id, so obviously I get an error for trying to create a composite index with a single field. I also tried it with two fields plus the document id, and sure enough the url generates a composite index for the two fields but leaving out the document id.
The composite indexing page in the firebase console also does not have an option to create a composite index involving the document id.
So it would seem to me that maybe using document id for sorting is not the intended practice? Should I create a unique id for each document for sorting purposes or if I can use document id for ordering how should I do it?
From the docs: "By default, a query retrieves all documents that satisfy the query in ascending order by document ID" (firebase.google.com/docs/firestore/query-data/…). So the behaviour you want to to achieve is what you get out of the box.
Related
I want to get a single Observable from a collection, but I want to get it from a different field that is not the id. It is possible?
I do not want to do a query and limit to 1. I need to get a Single Observable not an array Observable.
Schema:
Code:
this.afs.doc<Credit>('credits/uid/'+ uid).valueChanges();
Error:
Invalid document reference. Document references must have an even number of segments, but credits/uid/d1Zt8sozYqb6H27lhoJgF1Gx2Cc2 has 3
I am not sure if I understand correctly, but I guess that you want to get document with particular uid field value, not using document id.
This particular error is related with common feature of Firestore, that every document has to be in collection not in document. So path values for documents, (nested as well) are always checked, if the segments (devided by /) number is even ex. collection1/doc1/collection2/doc2/collection3/doc3
As results in your code we have 3 segments (like credits/uid/<uid_value>) so this is the error.
I am not very familiar with angularFire2 itself, but I have done it in JS. The approach is normally to query collection and than use method on the results, which in classic JS returns Query object on which the same methods can be used as on CollectionReference (which extends 'Query' btw - reference 1).
Combining this approach with those references: querying and collection I propose following solution:
this.afs.collection('credits', ref => ref.where('uid', '==', <uid_value>)).valueChanges()
If uid_value will be unique you should get your doc.
Unfortunately I do not have any playground to test the solution so please let me know how it works - or if there will be any additional errors.
I hope it will help! Good Luck!
I have a collection with shipments in them.
I want to filter on postalcode which is a part of the 'address_from' map.
Is this possible and are there extra steps required, indexes for example, to make this work?
query.where('address_from.postalcode', '==', shipment_code);
That query should just work. Any single field query should work without creating an index, as all fields are indexed by default. Queries that require an index will yield and error message telling you that one needs to be created, and provide a link to the console to automatically do that.
The chat app schema that I have is something like below.
1. conversations {participants[user_1, user_2], convsersation_id}
2. messages {sender: user_1, sonversation_id, timestamps}
I want to map this relationship using existing _id:ObjectId which is already indexed.
But if I want to get all conversation of user_1 I have to first search in which conversation that user is involed and get that conversation's _id and again search for the messages in messages using that conversation _id.
So my questions are -
Does length of indexed field (here _id) matters while searching?
Should I create another shorter indexed fields?.
Also if there is any better alternative schema please suggest.
I would suggest you to maintain the data as sub documents instead of array. The advantage you have is you can build another index (only) on conversation_id field, which you want to query to know the user's involvement
When you maintain it as array, you cannot index the converstaion_id field separately, instead you will have to build a multi key index, which indexes all the elements of the array (sender and timestamps fields) which you are never going to use for querying and it also increases the index size
Answering you questions:
Does length of indexed field (here _id) matters while searching? - Not really
Should I create another shorter indexed fields? - Create sub-document and index converstaion_id
Also if there is any better alternative schema please suggest. - Maintain the array fields as sub-documents
I'm trying to understand how Firestore creates indexes on fields. Given the following sample document, how are indexes created, especially for the maps/arrays?
I read the documentation at Index types in Cloud Firestore multiple times and I'm still unsure. There it says:
Automatic indexing
By default, Cloud Firestore automatically maintains single-field indexes for each field in a document and each subfield in a map. Cloud Firestore uses the following default settings for single-field indexes:
For each non-array and non-map field, Cloud Firestore defines two collection-scope single-field indexes, one in ascending mode and one in descending mode.
For each map field, Cloud Firestore creates one collection-scope ascending index and one descending index for each non-array and non-map subfield in the map.
For each array field in a document, Cloud Firestore creates and maintains a collection-scope array-contains index.
Single-field indexes with collection group scope are not maintained by default.
If I understand this correctly then there is an index created for each of these fields, even for the values in the alternate_names array.
So if I want to search for any document where fields.alternate_names contains a value of (for example) "Caofang", then Firestore would use an index for its search
Is my assumption/understanding correct?
No, your understanding is not correct. fields.alternate_names is an array subfield in a map field, which means it would not satisfy the requirements in the second point. You can test your assumption simply by issuing the query. If the query fails, you will see in the error message that it failed due to lack of index.
Firestore will simply not allow queries that are not indexed. The error message from that failure will contain a link to the console that will let you create the index necessary for that query, if such a thing is possible.
If you want to be able to query the contents of fields.alternate_names, consider promoting it to its own top-level field, which will be indexed by default.
Is there a way I can find the last inserted document and the field, i.e. _id or id such that I can increment and use when inserting a new document?
The issue is that I create my own id count, but I do not store this, now I've deleted records, I cannot seem to add new records because I am attempting to use the same id.
There is no way to check insertion order in MongoDB, because the database does not keep any metadata in the collections regading the documents.
If your _id field is generated server-side then you need to have a very good algorithm for this value in order to provide collision avoidance and uniqueness while at the same time following any sequential constraints that you might have.