How should a projection query be written in objectify, such that, the id of the entity also comes along in the result? (Projection query because my table has a lot of columns)
The query that I've written is
ofy().load().type(Item.class).filter("shopId",shopId)
.filter("name >=",name)
.filter("name <=",name+"\ufffd")
.order("-creationTime")
.project("name","imageUrl").list();
I've read putting id in the project function doesn't work. What's the workout to it, so that I get the name, imageUrl and the id as well?
My bad. The id does come along in the result. You don't need to put id in the project function.
Related
I've been reading a DynamoDB docs and was unable to understand if it does make sense to query on Global Secondary Index with a usage of 'contains' operator.
My problem is as follows: my dynamoDB document has a list of embedded objects, every object has a 'code' field which is unique:
{
"entities":[
{"code":"entity1Code", "name":"entity1Name"},
{"code":"entity2Code", "name":"entity2Name"}
]
}
I want to be able to get all documents that contain entities with entity.code = X.
For this purpose I'm considering adding a Global Secondary Index that would contain all entity.codes that are present in current db document separated by a comma. So the example above would look like:
{
"entities":[
{"code":"entity1Code", "name":"entity1Name"},
{"code":"entity2Code", "name":"entity2Name"}
],
"entitiesGlobalSecondaryIndex":"entityCode1,entityCode2"
}
And then I would like to apply filter expression on entitiesGlobalSecondaryIndex something like: entitiesGlobalSecondaryIndex contains entityCode1.
Would this be efficient or using global secondary index does not make sense in this way and DynamoDB will simply check the condition against every document which is similar so scan?
Any help is very appreciated,
Thanks
The contains operator of a query cannot be run on a partition Key. In order for a query to use any sort of operators (contains, begins with, > < ect...) you must have a range attributes- aka your Sort Key.
You can very well set up a GSI with some value as your PK and this code as your SK. However, GSIs are replication of the table - there is a slight potential for the data ina GSI to lag behind that of the master copy. If the query you're doing against this GSI isn't very often, then you're probably safe from that.
However. If you are trying to do this to the entire table at once then it's no better than a scan.
If what you need is a specific Code to return all its documents at once, then you could do a GSI with that as the PK. If you add a date field as the SK of this GSI it would even be time sorted. If you query against that code in that index, you'll get every single one of them.
Since you may have multiple codes, if they aren't too many per document, you maybe could use a Sparse Index - if you have an entity with code "AAAA" then you also have an attribute named AAAA (or AAAAflag or something.) It is always null/does not exist Unless the entities contains that code. If you do a GSI on this AAAflag attribute, it will only contain documents that contain that entity code, and ignore all where this attribute does not exist on a given document. This may work for you if you can also provide a good PK on this to keep the numbers well partitioned and if you don't have too many codes.
Filter expressions by the way are different than all of the above. Filter expressions are run on tbe data that would be returned, after it is already read out of the table. This is useful I'd you have a multi access pattern setup, but don't want a particular call to get all the documents associated with a particular PK - in the interests of keeping the data your code is working with concise. The query with a filter expression still retrieves everything from that query, but only presents what makes it past the filter.
If are only querying against a particular PK at any given time and you want to know if it contains any entities of x, then a Filter expressions would work perfectly. Of course, this is only per PK and not for your entire table.
If all you need is numbers, then you could do a count attribute on the document, or a meta document on that partition that contains these values and could be queried directly.
Lastly, and I have no idea if this would work or not, if your entities attribute is a map type you might very well be able to filter against entities code - and maybe even with entities.code.contains(value) if it was an SK - but I do not know if this is possible or not
Is it possible to query just part of the name and get the data
Like I have data 12345678
can I somehow just search for 1234?
data.whereEqualsto("data", 1234);
This is needed because the last numbers changes and the first ones doesn't.
Is it possible to query just part of the name and get the data Like I have data 12345678 can I somehow just search for 1234?
Sure it is. When it comes to Firestore, you can simply use .startAt() as seen in the following query:
db.collection("collName").orderBy("data").startAt(1234);
When it comes to the Realtime Database, you can use .startAt() too, but as seen below:
db.child("nodeName").orderByChild("data").startAt(1234);
But remember, both queries will return elements that are greater than 1234. Since 12345678 is greater, it will be present in the result set.
Im still new with DynamoDB , How do I query something based on the previous query result?
This is how my table look like :
I want to query for the list of project info for an user.
From my first query , the result of USER#001 have [PROJECT#001,PROJECT#002].
Then I want to get a list project detail based on the first query.
How do I make an "nested" query ?? or is there anyway there I can query more efficiently ?
*The table structure is fix, I cant change it.
You can't. That's not the way DDB works...
All you could do is a BatchGetItem() with the pk & sk for the two projects.
Or if you don't happen to know the SK, you'd need to make two individual Query() calls with the pk only.
Diesel's SqliteBackend does not implement the SupportsReturningClause trait, so the get_result method cannot be used to retrieve a newly created value.
Is there another way to find out the id of the inserted row? Python has a solution for this. The only solution I've found so far is to use a UUID for ids instead of an autoincrement field.
The underlying issue here is that SQLite does not support SQL RETURNING clauses which would allow you to return the auto generated id as part of your insert statement.
As the OP only provided a general question I cannot show examples how to implement that using diesel.
There are several ways to workaround this issue. All of them require that you execute a second query.
Order by id and select just the largest id. That's the most direct solution. It shows directly the issues with doing a second query, as there can be a racing insert at any point in time, so that you can get back the wrong id (at least if you don't use transactions).
Use the last_insert_rowid() SQL function to receive the row id of the last inserted column. If not configured otherwise those row id matches your autoincrement primary integer key. On diesel side you can use no_arg_sql_function!() to define the underlying sql function in your crate.
I have an issue in ydn db.
I need to fetch records by ids. Because it is not possible yet to say something like
"WHERE id IN (10, 11, 12)" you have to fetch id to id.
The problem comes here... I do not have to oppurtunity to sort fetched data by date with ydn db.
Now the question: Currently I sort the records with my own algorithm.
Is a indexeddb wrapper out there which is able to fetch records like my example above? If not so, is there a library which sorts an array of objects by given object key? (In my case it would be the date)
Thanks in advance. :-)
It is not possible. Not all sorted query are possible in IndexedDB. In this case, you have to resolve to in-memory sorting or using temporary object store. There is incomplete implementation ydn.db.Buffer to do this.