I'm querying two fields in a document. I'm using the whereIn(that's what it's called in flutter, for web it's called in) operator for one field. The other field I need to query is a string. And I want to query this value against two values. Do I need to separate the queries or is there a way to do the full query in a single query..
According to the Firestore documentation on query limitations:
You can use only one in or array-contains-any clause per query. You can't use both in and array-contains-any in the same query.
Since you need two whereIn/in clauses, you need to execute a separate query for each value in the second whereIn and then merge the results in your application code.
Related
I want to implement two where clauses in my flutter firestore query, so that they work as OR function. If any of the queries is true I want the result to show.
As the documentation states, Firestore DOES NOT HAVE an OR operation on where clauses. The closest you can come is 'in', which will check a single field against an array of values (up to 10 values). Otherwise, you will have to issue multiple queries and combine them in your application.
Please see current query operators supported.
This is what the cloud datastore doc says but I'm having a hard time understanding what exactly this means:
A projection query that does not use the distinct on clause is a small operation and counts as only a single entity read for the query itself.
Grouping
Projection queries can use the distinct on clause to ensure that only the first result for each distinct combination of values for the specified properties will be returned. This will return only the first result for entities which have the same values for the properties that are being projected.
Let's say i have a table for questions and i only want to get the question text sorted by the created date would this be counted as a single read and rest as small operations?
If your goal is to just project the date and text fields, you can create a composite index on those two fields. When you query, this is a small operation with all the results as a single read. You are not trying to de-duplicate (so no distinct/on) in this case and so it is a small operation with a single read.
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.
I have a mongodb query, and I want to add a computed field. The computed field is based on where or not the item is in the results of another query. So my query returns the columns a,b,c,d, and then column e should be based on whether or not the current row would be matched by another query.
Is there an efficient way to do this in mongo? I'm not really sure how to do this one...
There is no way currently to execute a function as you describe within the database when returning a document via standard functions such as find. It's been requested by the community, but the general request is to operate only on a single document.
There are calculated fields using $project in the aggregation framework. But, they only operate on the current document in the pipeline. So, they can't summarize other queries.
You'll need to likely build your e value as part of your data access layer.
I need to apply a set of filters (queries) to a collection. By default, the MongoDB applies AND operator to all queries submitted to find function. Instead of whole AND I need to apply each query sequentially (one by one). That is, I need to run the first-query and get a set of documents, run the second-query to result of first-query, and so on.
Is this Possible?
db.list.find({..q1..}).find({..q2..}).find({..q3..});
Instead Of:
db.list.find({..q1..}, {..q2..}, {..q3..});
Why do I need this?
Bcoz, the second-query needs to apply an aggregate function to result of first-query, instead of applying the aggregate to whole collection.
Yes this is possible in MongoDB. You can write nested queries as per the requirement.Even in my application I created nested MongoDb queries.If you are familiar with SQL syntax then compare this with in of sql syntax:
select cname from table where cid in (select .....)
In the same way you can create nested MongoDB queries on different collections also.