In loopback 4, I know we can limit records like this
?filter={"limit":10}
but what is the biggest value I can set as limit? Also is there a value I can put there which is the same thing as getting all records? Things like 0 or -1 don't work.
If limit is undefined, loopback will fetch all records.
Related
An example, a table with a column counter with only 1 row. I want to update this row's counter value based on its current value.
Say if counter is >= 10, set it to 0, otherwise counter++. How to achieve this if else clause in TransactWrite?
I can't have two actions in one transaction because Documentation states that it does not allow more than 1 action on the same item.
And of course, the reason I use TransactWrite is because there will be multiple lambda doing this task in parallel.
You cannot do it in one request, transactional or otherwise.
You can get the item, decide what to do, and then update the item in a second request accordingly. You’ll want to keep a version number or timestamp attribute to make sure the item hasn’t changed between the read and write, and use a condition expression to fail if it has.
That’s a common idiom:
https://dynobase.dev/dynamodb-locking/
You can't do it the way you like, because if/else is not supported in transactions. There is however a simpler solution.
Just Update the item and increment the counter. Whenever you read the value, you take the counter value modulo 10, and you get the desired behavior, e.g. 123 % 10 = 3 or 10 % 10 = 0.
In vtiger wiki written:
Query always limits its output to 100 records, client application can use limit operator to get different records.
This query does not work:
doQuery("select * from Leads limit='200';")
How to specify the operator in a query?
The "limit" clause only works if the number given is lower than 100. You can't get more records than 100 using "limit" with 1 request.
To get more than 100 records from vTiger services you need to make various request using the "offset" in the "limit" clause.
If you really read the Wiki documentation, you'd see that you need to use:
select *
from Leads
limit 200;
Stop using unnecessary single quotes ('200') - the limit expects a numerical value, there's absolutely no point in converting that to a string (by using single quotes) .....
and drop the equal sign, too - it's not shown in the docs anywhere .....
I have a small doubt regarding the READ capacity unit consumption when i query a dynamo db table with a LIMIT set on it.
Say my query expression could return 100 matching items if i iterate it with LastEvaluatedKey but if the limit is set to 20 and i dont iterate all pages( i want top 20 only) then how much read capacity unit will be consumed ? Is it going to be for 100 items or only for the retrieved 20 items?I have read the documentation but could not find anything clearly mentioning the paginated cases.
Here, throughput is the data sent over the network.
When you specify some limit (20 in your case) then only that number of rows are transfered at that time. And in case of no limit, maximum of 1 MB of data will be send.
Number of read capacity unit consumed on some query depends upon the size of your result.
In case of read operations - 4KB = 1 unit
and for write operations - 2KB = 1 unit.
For example if you query returned 15KB of data then your read units consumed will be - 15/4 = 4 read units.
The Limit parameter will tell DynamoDB how many items to examine. The Read Capacity Units consumed by that query will depend on the size of the items in your table. You will consume the RCU necessary for DynamoDB to look at the first 20 items.
If you are using a filter, you may not receive all 20 of those items. If you have a filter and you need 20 results, you will need to count the number of results and paginate until you have received 20 results. DynamoDB cannot do that counting for you.
Reference: DynamoDB Documentation for Limit
I'm currently working out if I will use DynamoDB for some of a Project. I want to know if I execute a query against the Database for a specific Key and it isn't found (eg: see if this UserID is present and get contents if it is) is this Query that returns no results considered a Read and Chargeable?
I expect I will do a certain amount of queries that won't return results (polling for information) and need to factor this in.
Below is from the AWS website: http://aws.amazon.com/dynamodb/pricing/
"Note that the required number of units of Read Capacity is determined by the number of items being read per second, not the number of API calls. For example, if you need to read 500 items per second from your table, and if your items are 1KB or less, then you need 500 units of Read Capacity. It doesn’t matter if you do 500 individual GetItem calls or 50 BatchGetItem calls that each return 10 items."
You can simply check it by calling DynamoDB and looking at ConsumedCapacityUnits in the result.
For example, if you are calling a simple getItem call for an item that exists, you get something like:
Result: {Item: {fans={SS: [Billy Bob, James], }, name={S: Airplane, }, year={N: 1980, }, rating={S: *****, }},
ConsumedCapacityUnits: 0.5, }
However, when you are calling it on an item that doesn't exist, you get:
Result: {ConsumedCapacityUnits: 0.5, }
Therefore, it appears that you are consuming your capacity even if the item is not in the table, as the lookup is running nevertheless
According to this link, there's a difference between Scan and Query operations. A query with no result will not result in any cost.
To provide a more specific answer, the query operation does get billed even if you don't get any results back (the accepted answer covers the getItem operation).
According to the current documentation, all items returned are treated as a single read operation, where DynamoDB computes the total size of all items and then rounds up to the next 4 KB boundary. Therefore, your 0 KB result would be rounded up to 4 KB and be billed as 0.5 or 1 read capacity unit, depending on your billing plan.
Below is a screenshot from my test database.
I have been querying Geonames for parks per state. Mostly there are under 1000 parks per state, but I just queried Conneticut, and there are just under 1200 parks there.
I already got the 1-1000 with this query:
http://api.geonames.org/search?featureCode=PRK&username=demo&country=US&style=full&adminCode1=CT&maxRows=1000
But increasing the maxRows to 1200 gives an error that I am querying for too many at once. Is there a way to query for rows 1000-1200 ?
I don't really see how to do it with their API.
Thanks!
You should be using the startRow parameter in the query to page results. The documentation notes that it takes an integer value (0 based indexing) and should be
Used for paging results. If you want to get results 30 to 40, use startRow=30 and maxRows=10. Default is 0.
So to get the next 1000 data points (1000-1999), you should change your query to
http://api.geonames.org/search?featureCode=PRK&username=demo&country=US&style=full&adminCode1=CT&maxRows=1000&startRow=1000
I'd suggest reducing the maxRows to something manageable as well - something that will put less of a load on their servers and make for quicker responses to your queries.