I have a relatively simple thing that I can do easily in SQL, but I'm trying to get used to using Lambda expressions, and having a hard time.
Here is a simple example. Basically I have 2 tables.
tblAction (ActionID, ActionName)
tblAudit (AuditID, ActionID, Deleted)
tblAudit may have an entry regarding tblAction with the Deleted flag set to 1.
All I want to do is select actions where we don't have a Deleted entry in tblAudit. So the SQL statement is:
Select tblAction.*
From tblAction LEFT JOIN tblAudit on tblAction.ActionID=tblAudit.ActionID
where tblAudit.Deleted <> 1
What would be the equivalent of the above in VB.Net's LINQ? I tried:
Context.Actions.Where(Function(act) Context.Audit
.Where(Function(aud) aud.Deleted=False AndAlso aud.ActionID=act.ActionID)).ToList
But that is really an inner join type scenario where it requires that each entry in tblAction also has an Entry in tblAudit. I am using Entity Framework Code First to do the database mapping. Is there a way to define the mapping in a way where you can do this?
You should add
Public Property Audits As DbSet<Audit>
into your action entity class (to register the association between those tables).
Now you can just write what you mean:
(From act in Context.Actions Where Not act.Audits.Any(Function(audit) audit.Deleted)).ToArray
which is equivalent to
Context.Actions.Where(Function(act) Not act.Audits.Any(Function(audit) audit.Deleted)).ToArray
and let the LINQ parser do the hard SQL work.
Related
I have been a Propel user for years and only recently started switching to Doctrine. It's still quite new to me and sometimes Propel habits kick in and make it hard form me to "think in Doctrine". Below is a specific case. You don't have to know Propel to answer my question - I also present my case in raw SQL.
Simplified structure of the tables that my query refers is like this:
Application table has FK to Admin which has FK to User (fos_user in the DB)
ApplicationUser table has FK to Application
My query gets all Application records with custom columns containing additional info retrieved from related User records (through Admin) and some COUNTs of related ApplicationUser objects, one of which is additionally filtered (adminname, usercount, usercountperiod columns added to the query).
I have a Propel query like this:
ApplicationQuery::create()
->leftJoinApplicationUser()
->useAdminQuery()
->leftJoinUser()
->endUse()
->withColumn('fos_user.username', 'adminname')
->withColumn('COUNT(application_user.id)', 'usercount')
->withColumn('COUNT(application_user.id) FILTER '
. '(WHERE score > 0 AND '
. ' application_user.created_at >= to_timestamp('.strtotime($users_scored['begin']).') and '
. ' application_user.created_at < to_timestamp('.strtotime($users_scored['end']).') )', 'usercountperiod')
->groupById()
->groupBy('User.Id')
->orderById('DESC')
->paginate( ....
This is how it translates to SQL (PostgreSQL):
SELECT application.id, application.name, ...,
fos_user.username AS "adminname",
COUNT(socialscore_application_user.id) AS "usercount",
COUNT(application_user.id) FILTER (
WHERE score > 0 AND
application_user.created_at >= to_timestamp(1491004800) and
application_user.created_at < to_timestamp(1498780800) ) AS "usercountperiod"
FROM application
LEFT JOIN application_user ON (application.id=application_user.application_id)
LEFT JOIN admin ON (application.admin_id=admin.id)
LEFT JOIN fos_user ON (admin.id=fos_user.id)
GROUP BY application.id,fos_user.id
ORDER BY application.id DESC
LIMIT 15
As you can see it's quite complex (in terms of translating it to Doctrine ORM, when you're a Doctrine newbie like me :) ). It uses specific features of PostgreSQL:
being able to include only Primary Key in GROUP BY statement, while other columns from the same table can be used in SELECT without aggregating function or inclusion in GROUP BY (because they are "dependent" on the PK);
FILTER which allows you to further filter records that are fed into aggregate functions
It also uses some joins and adds custom columns (adminname, usercount, usercountperiod) which I can access in my resulting Propel Model objects (with functions like $result->getAdminname().
My question is: what is the "Doctrine way" to achieve as similar thing as possible as simply as possible (use some PostgreSQL-specific or any RDBMS-specific features, add some custom columns which will be accessible through ORM objects and so on)?
Thank you for help.
I have a custom query along these lines. I get the list of orderIds from outside. I have the entire order object list with me, so I can change the query in any way, if needed.
#Query("SELECT p FROM Person p INNER JOIN p.orders o WHERE o.orderId in :orderIds)")
public List<Person> findByOrderIds(#Param("orderIds") List<String> orderIds);
This query works fine, but sometimes it may have anywhere between 50-1000 entries in the orderIds list sent from outside function. So it becomes very slow, taking as much as 5-6 seconds which is not fast enough. My question is, is there a better, faster way to do this? When I googled, and on this site, I see we can use ANY, EXISTS: Postgresql: alternative to WHERE IN respective WHERE NOT IN or create a temporary table: https://dba.stackexchange.com/questions/12607/ways-to-speed-up-in-queries-under-postgresql or join this to VALUES clause: Alternative when IN clause is inputed A LOT of values (postgreSQL). All these answers are tailored towards direct SQL calls, nothing based on JPA. ANY keyword is not supported by spring-data. Not sure about creating temporary tables in custom queries. I think I can do it with native queries, but have not tried it. I am using spring-data + OpenJPA + PostgresSQL.
Can you please suggest a solution or give pointers? I apologize if I missed anything.
thanks,
Alice
You can use WHERE EXISTS instead of IN Clause in a native SQL Query as well as in HQL in JPA which results in a lot of performance benefits. Please see sample below
Sample JPA Query:
SELECT emp FROM Employee emp JOIN emp.projects p where NOT EXISTS (SELECT project from Project project where p = project AND project.status <> 'Active')
I've written a SQL query that basically selects from a number of tables to determine which ones have rows that were created since a particular date. My SQL looks something like this:
SELECT widget_type FROM(
SELECT 'A' as widget_type
FROM widget_a
WHERE creation_timestamp > :cutoff
UNION
SELECT 'B' as widget_type
FROM widget_b
WHERE creation_timestamp > :cutoff
) types
GROUP BY widget_type
HAVING count(*)>0
That works well in SQL but I recently found that, while JPA may use unions to perform "table per class" polymorphic queries, JPQL does not support unions in queries. So that leaves me wondering whether JPA has an alternative I could use to accomplish the same thing.
In reality, I would be querying against a dozen tables, not just two, so I would like to avoid doing separate queries. I would also like to avoid doing a native SQL query for portability reasons.
In the question I linked to above, it was asked whether the entities that map to widget_a and widget_b are part of the same inheritance tree. Yes, they are. However, if I selected from their base class, I don't believe I would have a way of specifying different string constants for the different child entities, would I? If I could select an entity's class name instead of a string I provide, that might serve my purpose too. But I don't know if that's possible either. Thoughts?
I did a little more searching and found a (seemingly obscure) feature of JPA that serves my purpose perfectly. What I found is that JPA 2 has a type keyword that allows you to limit polymorphic queries to a particular subclass, like so:
SELECT widget
FROM BaseWidget widget
WHERE TYPE(widget) in (WidgetB, WidgetC)
I've found that JPA (or at least Hibernate as a JPA implementation) allows you to use type not only in constraints but also in select lists. This is approximately what my query ended up looking like:
SELECT DISTINCT TYPE(widget)
FROM BaseWidget widget
WHERE widget.creationTimestamp > :cutoff
That query returns a list of Class objects. My original query was selecting string literals because that's closest to what I might have done in SQL. Selecting Class is actually preferable in my case. But if I did prefer to select a constant based on an entity's type, that is the exact scenario that Oracle's documentation uses to illustrate case statements:
SELECT p.name
CASE TYPE(p)
WHEN Student THEN 'kid'
WHEN Guardian THEN 'adult'
WHEN Staff THEN 'adult'
ELSE 'unknown'
END
FROM Person p
Some JPA providers do support UNION,
http://wiki.eclipse.org/EclipseLink/UserGuide/JPA/Basic_JPA_Development/Querying/JPQL#UNION
but your query seems very complex, and non object-oriented, so using a native SQL query would probably be best.
THere is a oracle query that I am trying to recreate using OpenJPA. I am writing a service in Websphere integration developer, and I am using OpenJPA as my ORM tool of choice. Previously this query was performed using a stored proc, a ref cursor was used and the information was retrieved like that. Now we are trying to use OpenJPA as our tool of choice. So I am thinking that I should then reconstruct the stored proc using OpenJPA...
SELECT DISTINCT
P.col1 as ID,
P.col2,
P.col3,
P.col4,
P.col5,
S.col6,
PC.col7,
P.col8,
A.ADDRESS_1,
A.ADDRESS_2,
A.ADDRESS_3,
A.CITY,
A.COUNTY,
A.STATE,
A.ZIP_CODE,
P.CONFIRMED_BY,
P.CONFIRMED_DATE,
P.MOD_USERID,
P.MOD_DATE
FROM EPCD13.PROVIDER P, EPCD13.provider_channel PC, EPCD13.provider_channel_link pcl,
EPCD13.provider_specialty ps, EPCD13.SPECIALTY S, EPCD13.Address A, EPCD13.ADDRESS_LINK AL
WHERE P.RESOURCE_ID = personID
AND P.RESOURCE_ID = PS.RESOURCE_ID (+)
AND 1 = PS.PRIMARY_SPECIALTY_ID (+)
AND PS.SPECIALTY_ID = S.SPECIALTY_ID (+)
AND P.RESOURCE_ID = PCL.RESOURCE_ID (+)
AND PCL.PROVIDER_CHANNEL_ID = PC.PROVIDER_CHANNEL_ID
AND 1 = PCL.PREFERENCE (+)
AND 9 = pc.channel_type_id (+)
AND PC.CHANNEL_ADDRESS NOT LIKE '%#%'
AND P.RESOURCE_ID = AL.RESOURCE_ID (+)
AND AL.ADDRESS_ID = A.ADDRESS_ID (+)
AND 1 = A.ADDRESS_TYPE_ID (+)
AND 1 = AL.PREFERENCE (+);
Notice all those inner Joins and so forth. I am thinking right now of putting a named query in one my methods that will return the same results as above. As you may note, there are multiple tables that are being called there and joined at various points... I am thinking I can just put this query into the createNamedQuery() function with minor changes... But I am thinking there has to be a simpler way to do this? Maybe not. Can I just call a stored proc using JPA?
Because your SQL is very complex it's not easy to convert to JPQL, I suggest preserve it.
You can use OpenJPA's NativeQuery, which can do SQL query. If your SQL is not started with SELECT, it will be treated as stored proc.
You can create a JPA entity for each table and then join the entities by doing something similar to this:
http://openjpa.apache.org/builds/1.1.1-SNAPSHOT/docs/jpa_overview_mapping_full.html
Look at the #OnetoMany and #ManytoOne and #ManytoMany annotations in the example for some ideas.
I'm using Zend Framework for my website and I'd like to retrieve some data from my PostgreSQL database.
I have a request like :
SELECT DISTINCT ON(e.id) e.*, f.*, g.* FROM e, f, g
WHERE e.id = f.id_e AND f.id = g.id_f
This request works well but I don't know how to convert the DISTINCT ON(e.id) with Zend.
It seems that I can get DISTINCT rows but no distinct columns.
$select->distinct()->from("e")->join("f", "e.id = f.id_e")
->join("g", "f.id = g.id_f");
Any idea on how to make a select with distinct column ?
Thanks for help
You probably can't do this with Zend Framework since distinct on is not part of the SQL standard (end of page in Postgres documentation). Although Postgres supports it, I would assume its not part of Zend Framework because you could in theory configure another database connection which does not offer support.
If you know in advance that you're developing for a specific database (Postgres in this case), you could use manually written statements instead. You'll gain more flexibility within the queries and better performance at the cost of no longer being able to switch databases.
You would then instantiate a Zend_Db_Apdapter for Postgres. There a various methods available to get results for SQL queries which are described in the frameworks documentation starting at section Reading Query Results. If you choose to go this route I'd recommend to create an own subclass of the Zend_Db_Adapter_Pgsql class. This is to be able to convert data types and throw exceptions in case of errors instead of returning ambiguous null values and hiding error causes.