I am novice in Node.js. I want to implement pagination in my Api writing in Node.js using express as a framework and Postgresql as database. I want to get the data in form of pagination.
Thanks in advance.
You can use LIMIT and OFFSET in order to get chunks of data from the database. You need 2 variables to do the pagination, page and itemsPerPage. You'd get the page variable from the route itself, for example /api/items/:page, and for the itemsPerPage, you can make it default 20 items for example, but allow the clients to specify it through a query ?items=50 or the request body or a header or however you want. Then when you have both variables you can perform the query on the database, like:
SELECT *
FROM items
LIMIT {itemsPerPage} OFFSET {(page - 1) * itemsPerPage}
LIMIT means retrieve me X number of items, OFFSET means skip Y items. Both of them combined would be: "skip Y items and get me the next X items". Page - 1 means if you're on the 1st page we don't want to skip any items, but retrieve the first X items. This is valid when the page number is >= 1.
You can use indexes on columns used for sorting in pagination. Instead of limit & offset you can use where condition on column values (unique values) for efficiency. I have created a post regarding this https://medium.com/#shikhar01.cse14/pagination-with-postgresql-18e0b89e0b1c
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I would like to use Tabulator's remote pagination to load records from my database table, one page at a time. I expect that I should be able to use the page and size parameters sent by Tabulator to my remote back-end to determine which records to select from the database.
For example, with page=2 and size=10, I can use MySQL's LIMIT 10,20 to select the records to be shown on page 2 (if size is set to 10).
However, doing this precludes me from using the count of all records to determine the number of pages in the table. Doing a count on the returned records will only yield 10 records, even if there are a total of 500 records (for example), so only one pagination button will be shown (instead of the expected 50 buttons).
So in order to do remote pagination "correctly" in Tabulator, it seems I must do a query to count all records from my database (with no limits), then do a count to determine the last_page, and then do something like PHP's array_slice to extract the nth page's worth of records to return as the dataset. Or I can do 2 database queries: count all records to determine # of pages, and then do a LIMIT [start],[end] query.
Is this correct?
Tabulator needs to know the last page number in order to layout the pagination buttons in the table footer so that users can select the page they want to view from the list of pages.
You simply need to do a query to count the total number of records and divide it by the number of page size which is passed in the request. you can run a count query quite efficiently returning only the count and no data.
You can then run a standard query with a limit set on the records to retreive the records for that page.
If you want to optimize things further you could stick the count value in cache so that you dont need to generate it on each request.
I am developing an application (Python 3.x) in which I need to collect the first 13,000 results of a CSE query using one search keyword (from result index 1 to 13,000). For a free version of CSE JSON API (I have tried it), I can only get the first 10 results per query or 100 results per day (by repeating the same query while incrementing the index) otherwise it gives an error (HttpError 400.....returned Invalid Value) when the result index exceeds 100. Is there any option (paid/free) that I can deploy to achieve the objective?
Custom Search JSON API is limited to a max depth of 100 results per query, so you'll need to find a different API or devise some solution to modify the query to divide up the result set into smaller parts
Imagine situation when a client has feed of objects with limit 10.
When the next 10 are required it sends request with skip 10 and limit 10.
But what if there are some new objects were added (or deleted) to collection since the 1st request with offset == 0.
Then on 2nd request (with offset == 10) response may have wrong objects order.
Sorting on time of their creation does not work here, because I have some feeds which are formed on sorting via some numeric field.
You can add a time field like created_at or updated_at. It must updated when ever the document is created or modified and the field must be unique.
Then query the DB for the range of time using $gte and $lte along with a sort on this time field.
This ensures that any changes made outside the time window will not get reflected in the pagination, provided that the time field does not have duplicates. Most probably if you include microtime, duplicates wont happen.
It really depends on what you want the result to be.
If you want the original objects in their original order regardless of Delete and Add operations then you need to make a copy of the list (or at least of the order) and then page through that. Copy every Id to a new collection that doesn't change once the page has loaded and then paginate through that.
Alternatively, and perhaps more likely, what you want is to see the next 10 after the last one in the current set including any Delete or Add operations that have take place since. For this, you can use the sorted order in which you are viewing them and a filter, $gt whatever the last item was. BUT that doesn't work when there are duplicates in the field on which you are sorting. To get around that you will need to index on that field PLUS some other field which is unique per record, for example, the _id field. Now, you can take the last record in the first set and look for records that are $eq the indexed value and $gt the _id OR are simply $gt the indexed value.
I would like to iterate over all these documents without having to load the entire result in memory which seems to be the case apparently - QueryResponse.getResults() returns SolrDocumentList which is an ArrayList.
Can't find anything in the documentation. Am using SOLR 4.
Note on the background of problem: I need to do this when adding a new SOLR shard to the existing shard cluster. In that case, I would like to move some documents from the existing shards to the newly added shard(s) based on consistent hashing. Our data grows constantly and we need to keep introducing new shards.
You can set the 'rows' and 'start' query params to paginate a result set. Query first with start = 0, then start = rows, start = 2*rows, etc. until you reach the end of the complete result set.
http://wiki.apache.org/solr/CommonQueryParameters#start
I have a possible solution I'm testing:
Solr paging 100 Million Document result set
pasted:
I am trying to do deep paging of very large result sets (e.g., over 100 million documents) using a separate indexed field (integer) into which I insert a random variable (between 0 and some known MAXINT). When querying large result sets, I do the initial field query with no rows returned and then based on the count, I divide the range 0 to MAXINT in order to get on average PAGE_COUNT results by doing the query again across a sub-range of the random variable and grabbing all the rows in that range. Obviously the actual number of rows will vary but it should follow a predictable distribution.
Here is the case:
I need to display a list of records on a page, and paging is necessary. The question I got is whether a record should be displayed depends on validation result computed in memory, after selected from database.
for example, 50 records for one page:
Select 50 records from database
30 records are left after validation
Solution I have now it get all records from database, do validation and then get valid list of records. Paging is based on this list.
Is there any other good solution for this?
In the optimal case pagination can be divided in two steps. In the first step according to the selecting query a set of rows is selected from a database. All these rows could be displayed. Instead of fetching actual rows just retrieve a list of their identifiers. This list however large can be usually kept in memory. Second step is paging through the list by asking for n-th page of m items. Then only m rows are being completely retrieved from the database using their ids.
Additional step of computation is negating the idea of pagination that is having a list of identifiers of the whole result set.
What I can think of now without seeing the computation is to store results of computation in the database whenever a displaying row is being inserted/updated in the db. Since computation results depend from input parameters then for every row and for every range of input parameters you could have a different result.
This would then make paging possible. Performing the first step of paging should now include precomputed validation results and provide much faster retrieval of the list of row ids.