I have two collections where one collection is referencing another. Below is my structure:
CURRENCY_PAIR
CurrencyPair_Name
CurrencyPair_id
CURRENCY_PAIR_LIMIT
Limit_Currency_Pair_Id : CURRENCY_PAIR/0chTWgOpzolSxj590N1U <=makes a reference to the document in the CURRENCY_PAIR collection
Limit_Buy_Price_Threshhold
How can i query both collections such that when i get a currency pair, it is equal to the Limit_Buy_Price_Threshhold field that was added to the db with.
As provided on this thread, Firestore does not have a concept of server-side JOIN which is very near to what you want to achieve when you mentioned that you wanted to query both collections.
What I could think of is that you could remodel your database in a way that you can perform collection group queries. It works by putting CURRENCY_PAIR_LIMIT as a subcollection to the document in CURRENCY_PAIR.
Related
I'm trying to learn Datascript in the context of LogSeq, and I've stumbled into something I'm not sure how to solve.
The Fundamental Problem
I'm trying to query for a subset of entities that have NOT been referenced by attributes on a different group of filtered entities.
The Background
General LogSeq schema: https://github.com/logseq/logseq/blob/master/deps/db/src/logseq/db/schema.cljs
LogSeq Documentation for Datascript: https://docs.logseq.com/#/page/advanced%20queries
I've got a set of entities, with :block/properties like so:
tags:: contact
list:: C
Other entities have :block/refs to these pages.
I'm trying to create a query that shows me the contacts in a given list (A|B|C) that have NO notes within the past two weeks.
In SQL this would be a straightforward left join, but I'm having trouble translating that to Datalog since the information is in two different entity groups (instead of attributes all on the same entity). I assume there's some sort of not-join to filter out the contacts that have recent refs, but since that data is in other entities, I'm not sure how to structure the query since my implicit joins knock out either one group or the other.
I should add, because this is in LogSeq, I can't do two separate queries and join them in code. It has to be in one go.
Thank you!
I have recently started a firestore database. I was wondering is there any order in which the documents are added? is it just in the order they are created in?
There is no inherent sort order in which documents are stored, but you can specify the sort order you want to retrieve them in through the API. The documentation also contains a full table on how data is sorted.
If you're asking about the Firestore console, that by default orders the documents on their IDs, but you can change that by clicking the filter button at the top of the list of document IDs.
I am trying to think of a way to design the firestore db in a way that is efficient.
The main issue I am having with is how I should define "groups". Lets say a user is invited to a group chat and so the client needs to retrieve the data for that group chat, should I have a "groups" collection and then find the correct group document? OR, should I have a "groups" property in the user document that has a id to reference the group to retrieve?
In SQL, having a reference in a user's groups table would be the obvious answer, but I am not sure about firestore. I don't want to look through the entire collection of groups just to find the group that the user was newly invited in. Any tips? Also, my front end is in React and I am considering using the onSnapshot method to subscribe to the collection (that seems to be the best way to have real time updates).
What i believe is best for you is this :
First have a collection, suppose you make groups, and inside that every docuent has all the group unique ids,
And inside that for every group, i.e document, you can have a collection which holds all the chats for that group and group related info , like group type, etc etc
Hope it helps. feel free for doubts
I'm trying to fetch a long list of entities, and those entities all refer to one of a few different related entities. It's explained in the comments, but basically many "items" reference to a few "Company"s. I don't want to have to make multiple queries for each key in unique_key (IE key.get()), so I thought the following would work but it's returning an empty list. Pray tell, what am I doing wrong? Or is there a better way to accomplish this relationship of many items referencing a few, while minimizing calls to the db (I'm new to AppEngine Datastore).
Notice, this is in Python, using the ndb library offered by app engine.
# "items" is a list of entities that have a property "parenty_company"
# parent_company is a string of the Company key
# I get a unique list of all Key strings and convert them to Keys
# I then query for where the Company Key is in my unique list
unique_keys = list(set([ndb.Key(Company, prop.parent_company) for prop in items]))
companies = Company.query(Company.key.IN(unique_keys)).fetch()
You definitely should use ndb.get_multi(unique_keys). It will fetch all keys asynchronously in a single batch.
I need to do some continuous aggregation on a data set. I am using app engines High Replication Datastore.
Lets say we have a simple object with a property that holds a string of the date when it's created. There's other fields associated with the object but it's not important in this example.
Lets say I create and store some objects. Below is the date associated with each object. Each object is stored in the order below. These objects will be created in separate transactions.
Obj1: 2012-11-11
Obj2: 2012-11-11
Obj3: 2012-11-12
Obj4: 2012-11-13
Obj5: 2012-11-14
The idea is to use a cursor to continually check for new indexed objects. Aggregation on the new indexed entities will be performed.
Here are the questions I have:
1) Are objects indexed in order? As in is it possible for Obj4 to be indexed before Obj 1,2, and 3? This will be a issue if i use a ORDER BY query and a cursor to continue searching. Some entities will not be found if there is a delay in indexing.
2) If no ORDER BY is specified, what order are entities returned in a query?
3) How would I go about checking for new indexed entities? As in, grab all entities, storing the cursor, then later on checking if any new entities were indexed since the last query?
Little less important, but food for thought
4) Are all fields indexed together? As in, if I have a date property, and lets say a name property, will both properties appear to be indexed at the same time for a given object?
5) If multiple entities are written in the same transaction, are all entities in the transaction indexed at the same time?
6) If all entities belong to the same entity group, are all entities indexed at the same time?
Thanks for the responses.
All entities have default indexes for every property. If you use ORDER BY someProperty then you will get entities ordered by values of that property. You are correct on index building: queries use indexes and indexes are built asynchronously, meaning that it's possible that query will not find an entity immediately after it was added.
ORDER BY defaults to ASC, i.e. ascending order.
Add a created timestamp to you entity then order by it and repeat the cursor. See Cursors and Data Updates.
Indexes are built after put() operation returns. They are also built in parallel. Meaning that when you query some indexes may be build, some not. See Life of a Datastore Write. Note that if you want to force "apply" on an entity you can issue a get() after put(), which will force the changes to be applied (= indexes written).
and 6. All entities touched in the same transaction must be in the same entity group (=have common parent). Transaction isolation docs state that transactions can be unapplied, meaning that query after put() will not find new entities. Again, you can force entity to be applied via a read or ancestor query.