I have a case where I am given 2 IDs and there are 2 columns,assuming names'subj'and 'obj' in a table.If the Id's dont match in a single row, then i have to take the obj value and search for its entry in some other row in the subj column and then try to match the object iteratively. the search ends when there is no subject entry for a particular object. There is no with clause in hql and hence this question.
Example lets say i am given 1,100. Then i have to search for 1 and then get its object entry, if it is not 100 and lets say it is 20, i have to take that 20 and search for 20,100 , and once again it is not 100 in object entry, i have to repeat the process. This is possible in sql, but since there is no with clause in HQL i need suggestions.
I can always do it in the application but i am looking for another answer! The search ends when there is no corresponding subject entry for an object entry, or when it matches.
You need recursion for this, which is supported by some database implementations, but not by hql
HQL recursion, how do I do this?
Related
I have a table 'ACCOUNTS', with fields ACCTNO and ACPARENT. One account can be the parent of another. One account can have many children.
It's been discovered that certain external processes are using the 'first child' in certain reports and outputs - but there's no actual 'reason' for any particular child to be 'first', just an unintended bug in the code.
First step in untangling this - I need a query, that can be re-run (but not often, so optimisation is not really a factor) that will identify, for all accounts that are parents, what their 'first child' is.
Problem - the 'first child' isn't necessarily anything to do with record ID. If I run the following query, for example:
SELECT ACCTNO FROM ACCOUNTS WHERE ACPARENT = '80005217';
I get a result of:
ACCTNO
______
80007325
80007310
80007315
80007298
I can absolutely, 100% confirm that for this particular example, account 80007325 is the account ID being used as the 'first child'.
On the flipside, if I run a naive query of:
SELECT A1.ACCTNO, A2.ACCTNO AS CHILDACCOUNT FROM ACCOUNTS A1
INNER JOIN ACCOUNTS A2 ON A1.ACCTNO = A2.ACPARENT
WHERE A1.ACCTNO IN
(SELECT ACPARENT FROM ACCOUNTS);
then if I scroll down to where 80005217 is the parent account, I see the following list:
CHILDACCOUNT
______
80007298
80007310
80007315
80007325
It's sorted, even though it's exactly not what I want.
Is there a query that will get me a list of what I want in a single query? A list of all parent accounts, and their 'first child' as returned by SQL unsorted?
To guarantee records coming in a fixed order we must provide the database with sort criteria in the ORDER BY clause. If there is no attribute which defines "first-ness" then no guarantee is possible. Without an ORDER BY clause the records are essentially in an uncontrolled order, although because of
database internals they often fall into some kind of pattern.
So, what makes account 80007325 the first child WHERE ACPARENT = '80005217'? Clearly not numerical order. Is there some other criterion? Date created? A flag column? Seems like you need to talk to your users. Do they really care which records come first? All the time or just in some specific report?
If your users cannot specify the criteria there's not much you can do...
...although I might be tempted to sort CHILDACCOUNT numerically by ACCTNO whenever it is displayed. At least that would provide consistency, and the users will get used to it.
I am using solr to do a search. As result I get back a set of fields. One of the fields is "domains". The domain field is a many to many relationship in my database, so my docs contain an array of "domains" the are linked to.
What I want to do is, for each domain in the resultset, count how many times this "domain term" is found in the global result set.
How should I do this ?
You need to look at the Field collapsing feature.
I have a bunch of records in my database which all have the same Title but different Locations. Once I filter by within a location boundary, I want to filter out ones with the same Title. Is there an ActiveRecord way to do this? I know about select, but that will only return titles, and I actually need the entire record.
So I have a Business which has a Title. If I select all of the businesses within a given lat/long boundary, multiple instances with the same name (say, Subway) will be returned. I want to limit the result to 10.
In English: Given me ten records (the entire record, not just certain columns) where every title is unique amongst the ten returned.
You can simply use .first, i.e.
Venue.where(name: "Subway").first
If you need more than one element, pass a parameter to first:
Venue.where(name: "Subway").first(10)
To select one entry per distinct value in some column, you can use .group("column_name"):
Venue.where(some_condition).group("name")
ModelName.where(title: "Building")
If you provide a more specific question, I'll provide a more specific answer...
I am having a problem trying to achieve the following:
I'd like to have a page with 'infinite' scrolling functionality and all the results fetched to be sorted by certain attributes. The way the code currently works is, it places the query, sorts the results, and displays them. The problem is, that once the user reaches the bottom of the page and new query is placed, the results from this query are sorted, but in its own context. That is, if you have a total of 100 results, and the first query display only 50, then they are sorted. But the next query (for the next 50) sorts the results only based on these 50 results, not based on the 100 (total results).
So, do I have to fetch all the results at once, sort them, and then apply some pagination logic to them or there's a way for MongoDB to actually have infinite scrolling (AJAX requests) with sorting applying to the results?
There's a few ways to do this with MongoDB. You can use the .skip() and .limit() commands (documented here: http://www.mongodb.org/display/DOCS/Advanced+Queries#AdvancedQueries-CursorMethods) to apply pagination to the query.
Alternatively, you could add a clause to your query like: {sorted_field : {$gt : <value from last record>}}. In other words, filter out matches of the query whose sorted value is less than that of the last resulting item from the current page of results. For example, if page 1 of results returns documents A through D, then to retrieve the next page 2 you repeat the same query with the additional filter x > D.
Let me preface this by saying that I have no experience with MongoDB (though I am aware that it is a NoSQL database).
This question, however, is somewhat of a general database one (you'd probably get more responses tagging it as such). I've implemented such a feature using Cassandra (another, albiet quite different NoSQL database), however the same principles apply.
Use the sorted-by attribute of the last retrieved record, and conduct a range search based on it in the database. So, assuming your database consists of the following set of letters:
A
B
C
D
E
F
G
..and you were retrieving 2 letters at a time, you'd retrieve A, B first. When more records are needed, you'd use B to conduct a range search on the set of letters in the database. In plain English this would be something like:
Get the letters that appear after B, limit the results to 2
From a brief look at the MongoDB tutorial, it looks like you have conditional operators to help you implement this.
I want to know the best way of testing data access functionality.
I know that it is possible to create mocks to change data layer objects that is using to test business logic.
However is it possible to test if sql queries to database are correct.
Scenario: A method must return employees which were applied for work last month.
I can return list of object and check if each employee's startDate property is correct (last month).
So if it returns 3 employees and they have correct startDate value but there are more two employee in database which aren't returned. How to write test for that case? :)
Thanks in advance.
You set up the test DB so you shold know what data is in it. If you expect 5 employees to be returned from the query and you get only 3, you know there is an error.
You can test the query with different setups: empty table, only new employees, only old employees, a mix of the two (with special care to the borderline cases), etc.
I don't think you need to check the two other employees in the database which aren't returned.
The key is, when setting up your test data, you would want to ensure you have enough records that don't match the criteria (in addition to the records that do match), then you run the fetch and make sure you get back the correct number of records that do match the criteria.
Preparing the test data in this manner ensures that your method is returning the expected results.