JPA query language syntax

My question is if JPA query language syntax allows full qualified class names in the SELECT clause of the query, e.g.:
SELECT * FROM com.abc.Person
This works well with Hibernate, but TopLink Essentials complains about the dots in com.abc.Person.
In the Java EE 5 Tutorial only partially qualified names ( SELECT * FROM Person) are used.
There are only examples with fully qualified names for constants in WHERE clauses.

my first guess:
SELECT t FROM tablename t WHERE t.timestamp>:somethingwhere :something
is handled with something like: (..).setParameter("something", someSQLDate);

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Persistence Query language

hi guys
I am using persistence query language, I'm trying to delete an entry from the database table. So far I tried 2 approaches
public void destroy(DeviceType deviceType)
em.merge(deviceType);
em.remove(deviceType);
public void delete(int pk)
em.createQuery("Delete from DeviceType dt where dt.deviceTypeID = '"+pk+"'");
both of these methods are not working for me.
please help

Hi shim1,
1. If you're executing destroy in an extended persistence context, em.merge(deviceType) is not needed. In a transaction scoped persistence context, you must change destroy to:
public void destroy(DeviceType deviceType)
DeviceType mergedType = em.merge(deviceType);
em.remove(mergedType);
Please see chapter 3.2.4.1 of the JPA specification for more information about the merge operation.
2. Please change the delete method to:
public void delete(int pk)
em.createQuery("Delete from DeviceType dt where dt.deviceTypeID = ?1").setParameter(1, new Integer(pk)).executeUpdate();
}

Applying a query language to collections

Hi, we handed in a project a while ago that was essentially to read in data from a .DAT file, store it in appropriate collections, then use a basic query language to filter through the stored data. I wasn't really happy with my querying though, as it was basically a huge succession of control statements. The queries were of the form "select OBJECTNAME where ATRIBUTE OPERATOR VALUE and ATRIBUTE OPERATOR VALUE", there could be as many sub clauses as desired (0... 200 whatever). For example "select elephant where height > 360 and weight <= 1000".
We had a comment back that we should use a Query interface and a two subclasses to represent a simple query (e.g. height > 360) and then a conjunctive query (ie simplequery1 AND simplequery2 ). The Query interface would then have a match method. I'm struggling to get my head around how I do this, does anyone have a simple example or explaination that might help me out?
Cheers.

I've done something like this a couple times. Your need to get a better idea of what you want your query language to look like. For example, if you're given a list of elephants, the "select elephant" part is unnecessary (your query will just return a list of matching elephants). You should decide if you want it to handle things like (height > (weight / 2)), whether conditions can be nested "((a and b) or (c and d)) and (e or f)". Will you need to support the conditional operator (a ? b : c) or a unary operator (-)? How complex will your order of operations rules be?
If you keep it simple (always two operands), you could go with something like this:
public interface QueryOperator
public boolean eval(Object leftParam, Object rightParam);
public enum BasicOperators implements QueryOperator
public class QueryElement
private QueryOperator operator;
private Object leftParam;
private Object rightParam;
}

General JPA query question

Hello world,
I'm new to JPA 2.0 and there are few things I don't understand.
BTW: I can't figure out the keywords to search for this question, so please pardon me if it's one of the most asked.
Using the Preview, I've seen that alignment went straight to Hell, so I tried to make this as readable as I could using pipes in place of white spaces in the result sets.
I have a couple of tables:
CUST table (for customers):
CUST_ID (pk, integer)
CUST_NAME (varchar)
ORD table (for orders):
ORD_ID (pk, integer)
ORD_STATUS (char) can be: N for new, S for shipped, D for delivered
CUST_ID (fk, integer)
The relationship is, of course, a "one to many" (every customer can place many orders).
Content of the tables:
CUST_ID|CUST_NAME
1|elcaro
2|tfosorcim
3|elppa
ORD_ID|ORD_STATUS|CUST_ID
2|N|1
3|N|1
4|N|1
5|S|1
6|S|1
7|D|1
8|D|1
9|D|1
10|D|2
11|N|2
12|S|3
13|S|3
Here's how I annotated my classes:
Customer.java:
@Entity(name = "Customer")
@Table(name = "CUST")
public class Customer implements Serializable
private static final long serialVersionUID = 1L;
@Id
@Column(name = "CUST_ID")
private Integer id;
@Column(name = "CUST_NAME")
private String name;
@OneToMany(mappedBy = "customer")
private List<Order> orders;
// Default constructor, getters and setters (no annotations on these)
Order.java:
@Entity(name = "Order")
@Table(name = "ORD")
public class Order implements Serializable
private static final long serialVersionUID = 1L;
@Id
@Column(name = "ORD_ID")
private Integer id;
@Column(name = "ORD_STATUS")
private Character status;
@ManyToOne
@JoinColumns
@JoinColumn(name = "CUST_ID", referencedColumnName = "CUST_ID")
private Customer customer;
// Default constructor, getters and setters (no annotations on these)
Everything works just fine, the following JPQL query yields the results I expected:
select c from Customer c
it returns three objects of type Customer, each of which contains the orders that belong to that customer.
But now, I want to extract the list of customers that have orders in status 'N', along with the associated orders (only the status 'N' orders, of course).
Back in the good ol' days I would have written an SQL query like this:
select c.cust_id, c.cust_name, o.ord_id, o.ord_status
from cust c
inner join ord o on (o.cust_id = c.cust_id)
where o.ord_status = 'N'
and it would have returned the following result set:
CUST_ID|CUST_NAME|ORD_ID|ORD_STATUS
1|elcaro|2|N
1|elcaro|3|N
1|elcaro|4|N
2|tfosorcim|11|N
The following JPQL query, however, doesn't yield the expected results:
select distinct c from Customer c join c.orders o where o.status = 'N'
it returns the correct set of customers (customer 'elppa' doesn't have any status 'N' order and is correctly excluded), but each customer contains the full set of orders, regardless of the status.
It seems that the 'where' clause is only evaluated to determine which set of customers has to be extracted and then the persistence provider starts to navigate the relationship to extract the full set of orders.
Thinking a little about it, I must admit that it makes sense.
I then tried out another JPQL query:
select c, o from Customer c join c.orders o where o.status = 'N'
this JPA query yields results that are similar to the ones produced by the previous SQL query: each result (4 results as expected) is a 2-object array, the first object is of type Customer and the second object is of type Order. But, again, the objects of type Customer contain the full set of related orders (as I expected, this time). Not to mention the fact that now the orders are not contained in the Customer objects, but are returned separately, just as in an SQL result set.
Now the question is:
Is it possible to write a JPA query that filters out, not only the customers that don't have an order in status 'N', but the related orders (fetched during relationship navigation) that are not in status 'N' as well?
What I'd like to be able to get is a 2-customer result where each customer contains only its status 'N' orders.
I read the Java EE 6 Tutorial and one of the examples (the Order Application) has a schema that is similar to mine, but I couldn't find a query like this (in the downloaded source code).
Although I think the above is standard behavior, I use an Oracle Weblogic 12c server (through its Eclipse adapter) and the persistence provider appears to be EclipseLink.
Thanks in advance.
Best regards,
Stefano
Edited by: user11265230 on 17-apr-2012 14.11

Hello,
When returning an entity from JPQL, it gives you the entity as it is in the database. Your "select distinct c from Customer c join c.orders o where o.status = 'N'" is asking for all customers that have an order with a status of 'N', so that is what it gives you. There is no condition to filter anything on the relationship when building the Customer object in JPA - doing so would mean returning a managed entity that does not reflect what is in the database. This would affect other queries, since JPA requires that queries return the same instance of an entity regardless of the query that is used to bring it back. So a query using your "where o.status = 'N'" would cause conflicting results when used with a query using "where o.status = 'Y'". And these queries would make the EntityManager unable to determine what has changed on the returned objects.
EclipseLink does have the ability to filter over relationships, it is just not available through standard JPA and I would strongly discourage it. Instead of querying for Customers, why not change the query to get Orders instead -
"select o from Customer c join c.orders o where o.status = 'N'". Assuming Orders have a ManyToOne back reference to their Customer, this will mean you do not need to travers the Customer-> order relationship. If using
"select c, o from Customer c join c.orders o where o.status = 'N'"
I am not sure why you would use the orders from the returned customers instead of the orders returned in the results though.
You could also return "select c.id, c.name, o.id, o.status from Customer c join c.orders o where o.status = 'N'" which is the equivalent of what you would get from the SQL you initially posted.
Regards,
Chris

How to configure lazy/eager loading for each JPA query

Hi!
I have extensive EJB model (entities with many child entities, entities with association to other large (many fields, BLOBs including) entities, and so on) and I would like for each JPA query configure what properties or associated entities (actually - in arbitrary depth) of selected entities should be fetched.
E.g. for one query I would like to fetch only Order (and no data of associated entities), but for other queries I would like to fetch Order, Order.Customer, Order.ShippingAddress.ZipCode and nothing else ( e.g. if there is Ordere.Route, Order.Billing and other associations, then I would like not to waste resources for fetching them). In both case the select clause of query can include only Order, but the results should be different - i.e. - there is no associated data in the first case and there are some associated data the second case.
I know that one solution is to declare all associations as lazy and then - after reading the result of query - do some touching for retrieving the associated data:
String check = order.Customer.toString();
check = order.ShippingAddess.ZipCode.toString();
But I see 2 problems with this: 1) it is not nice (resources are wasted for simply touching associated entities); 2) I assume that each "touch" operation generates other query to database that could be executed together with the original query. So - it would be nice to configure JPA query somehow to let it know which associations will be required from the result and which not.
What is the best practice?
I found, that JBoss server has lazy-loading-group configuration, but - I guess - it is JBoss specific:
http://docs.redhat.com/docs/en-US/JBoss_Enterprise_Application_Platform/4.2/html/Server_Configuration_Guide/Loading_Process-Lazy_loading_Process.html
besides - it is XML and it would be more pretty if query configuration could be done with annotations!

JPQL has a "fetch" construct in which you can force a lazy element to be fetched using a query - I must note that I have had unexpected results with it in the past but that was using an old version of Hibernate and I wasn't very experienced with JPA yet.
http://docs.oracle.com/cd/E15051_01/wls/docs103/kodo/full/html/ejb3_langref.html#ejb3_langref_fetch_joins

XPath Query Language Reference

Aside from the three little examples given in the 11g Guide and the B2B Tech Note #011, is there a reference available for the XPath Query Language used by B2B? Is is possible to use complex XPath queries in the B2B Doc Definitions?

I'm mainly just looking for the full capabilities of the queries.
Specifically, at the moment, I'm looking for a way to match the value of a node to a group of values (like a sql 'in') as well as check the existence and value of other nodes within the same query.
Do the documents I find for 'Preference XPath' pertain here?

EJB Query Language

Hi All,
I am using SAP Netweaver Developer Studio(2004)version.I want to know that EJB2.0 Query Language will
support Joins,Internal select statement with in a select
statement or not.Is it posssible or not.I have a requirement lilke this,I have to use joins.
Thanks & Regards,
Guru

Guruvulu,
In EJB QL you may operate on objects relations (both 0..1 and 0..n) in the same way as with joins in SQL. So the answer is yes.
Read free <a href="http://www.theserverside.com/books/wiley/masteringEJB/downloads/MasteringEJB3rdEd.pdf">Mastering EJB</a> book -- it contains separate chapter on EJB QL.
Valery Silaev
EPAM Systems
http://www.NetWeaverTeam.com

EJB Query Language where condtion based on date

Hi,
I am using EJB3 query language. In the table I have a column called requestdate which is in date time format. I have created an entity class.
I need to select few records using query language(named queries) based on this requestdate matching to the current date. I want to compare only based on Date value (truncating the time). Something like this
select max(o.req_id) from requests o where o.requestdate = :currentdate
currentdate is java.sql.Date value formatted to yyyymmdd only.
How can I do this using query language?
Please help to me get this done.
thanka
Anuradha

Hi Anuradha ,
I'm afraid the query language does not support retrieving the date portion (i.e. truncating the time) from a date field.
I propose you turn you named into a BETWEEN query taking two parameters one for the beginning of the day and another for the end of the day. Then your named query could look like:
SELECT max(o.req_id) FROM requests o WHERE o.requestdate BETWEEN :start AND :end
The following code creates two calendar instances for the current day, one for 00:00:00 and another for 23:59:59:
Calendar start = Calendar.getInstance();
start.set(Calendar.HOUR_OF_DAY, 0);
start.set(Calendar.MINUTE, 0);
start.set(Calendar.SECOND, 0);
start.set(Calendar.MILLISECOND, 0);
Calendar end = Calendar.getInstance();
end.set(Calendar.HOUR_OF_DAY, 23);
end.set(Calendar.MINUTE, 59);
end.set(Calendar.SECOND, 59);
end.set(Calendar.MILLISECOND, 999);
Here is some sample code that creates a query instance for a named query called findMaxRequestPerDay and passes the Date of the above Calendar instance as actual parameter values. It assumes the named query is called findMaxRequestPerDay and the req_id field is a long:
Query query = em.createNamedQuery("findMaxRequestPerDay");
query.setParameter("start", start.getTime());
query.setParameter("end", end.getTime());
Long max = (Long)query.getSingleResult();
I hope this helps.
Regards Michael

EJB query language help!!

Hi all, I have been trying to run a ejb query on JBoss 4.0.5, using built in hypersonic db, For some strange reasons am able to fetch all objects from db without any where clause but if am using a where clause with an attribute name from the entitybean am unable to retrieve any results.
I get an org.hibernate.QueryException, could not resolve property : "property name"
My ejb query looks like this...
SELECT template FROM TemplateSelect template WHERE template.template_name='Template_One'
TemplateSelect is my entity bean class and I do have an attribute named template_name in my bean class.
could any one please suggest me what could be wrong and also direct me to a good tutorial on ejb query language as well as I am fairly new to hibernate and ejb3 !
tons of thanks in advance!
pravin

Hi Anuradha ,
I'm afraid the query language does not support retrieving the date portion (i.e. truncating the time) from a date field.
I propose you turn you named into a BETWEEN query taking two parameters one for the beginning of the day and another for the end of the day. Then your named query could look like:
SELECT max(o.req_id) FROM requests o WHERE o.requestdate BETWEEN :start AND :end
The following code creates two calendar instances for the current day, one for 00:00:00 and another for 23:59:59:
Calendar start = Calendar.getInstance();
start.set(Calendar.HOUR_OF_DAY, 0);
start.set(Calendar.MINUTE, 0);
start.set(Calendar.SECOND, 0);
start.set(Calendar.MILLISECOND, 0);
Calendar end = Calendar.getInstance();
end.set(Calendar.HOUR_OF_DAY, 23);
end.set(Calendar.MINUTE, 59);
end.set(Calendar.SECOND, 59);
end.set(Calendar.MILLISECOND, 999);
Here is some sample code that creates a query instance for a named query called findMaxRequestPerDay and passes the Date of the above Calendar instance as actual parameter values. It assumes the named query is called findMaxRequestPerDay and the req_id field is a long:
Query query = em.createNamedQuery("findMaxRequestPerDay");
query.setParameter("start", start.getTime());
query.setParameter("end", end.getTime());
Long max = (Long)query.getSingleResult();
I hope this helps.
Regards Michael

Query language for CTXRULE MATCHES

I am trying to build an alerting application when, on receipt of a new XML document, user's are alerted if the document matches one or more of the profiles that they have defined. I have created a CTXRULE index that does this but only with very simple profiles. For example ABOUT(soccer), which is the example in the Text documentation.
Is it possible to create more complex queries, for example using WITHIN to only match within defined elements of the XML document. Is there a definition of the query language that can be used with MATCHES and are there any good example?
Thanks
Martin Haigh

Omar,
Thanks for the reply. I had actually found that document myself but I couldn't get the WITHIN clause to work and that document conflicted with the ORACLE documentation at:
<a href="http://download-west.oracle.com/docs/cd/B10501_01/text.920/a96517/ind.htm#1010647> Do you have any examples of using WITHIN?
Thanks
Martin

Query language for XML documents

Which is a better (efficiency in terms of memory management) query language for interacting with XML documents.The query language shouls support 'insert', 'delete', 'update' and 'select' commands. How fast is database as compared to XML ( database being replaced by XML) when only 'insert' n 'select' commands are issued?

Hi,
I suggest you use the Sunopsis JDBC for XML driver that will let you perform all kind of SQL statements on your XML files. It is a type 4 driver so it's very use to use. You may have more information and download it here:
http://www.sunopsis.com/corporate/us/products/jdbcforxml/
Hope that will help
Simo Fernandez

Query language for XML that is going to remove use of database

Friends,
I want to know whether my idea is feasible or not.
I want to make a query language similar to SQL for XML which is going to remove the need for database for a large extent.
Their will be queries for making table,extracting data,making foreign key all through XML and no database.
I just want to know that is their any market value for such a project and will it be sellable,so that i can start working on it.

There is no way to judge any future market for such a thing.
As it is, XML is widely abused, having mutated from its original purpose, a markup language readable by both machine and human, to a general data interchange language. It winds up being extremely slow and convoluted, in some cases overwhelming the hardware when a simple and common error occurs, then having to catch up. A big part of this is the silly and redundant method of defining metadata, again and again and again and again.
So what you want to do is create a database which will be highly formatted with redundant information, dynamically. This is silly, why does data need to be stored in a human readable format? It doesn't always even need to be presented in a human readable format! Why the heck would you need to read the bits of an mp4? Steganography?
What you are proposing is the exact opposite of what is needed. What is needed is a way to describe metadata for many different kinds of data, in a manner that can be interpreted by both man and machine at appropriate times, extensible for various paradigms.
What can be sold, on the other hand, is another question entirely, and not technical at all.
First definition of database that pops up during a search: an organized body of related information
Why would you want to get rid of that?

DRG-50901: text query parser syntax error

The query
SELECT * FROM ij
where
CONTAINS (ij.summary, 'ATTENZIONE!') > 0 returns an error:
ORA-29902: error in executing ODCIIndexStart() routine
ORA-20000: Oracle Text error:
DRG-50901: text query parser syntax error on line 1, column 13
Why?
There is a TEXT index on the summary column:
CREATE INDEX IJL_SUMMARY_IX ON IJ
(SUMMARY)
INDEXTYPE IS CTXSYS.CONTEXT
PARAMETERS('
    lexer           MITO_LEXER
    wordlist        DEFAULT_WORDLIST
    stoplist        IJL_STOPLIST
    storage         IJL_TEXT_STORAGE
    SYNC (EVERY "SYSDATE + 10/1440")')
PARALLEL ( DEGREE 4 INSTANCES 1 );where the MITO_LEXER is
BEGIN
CTX_DDL.create_preference ('mito_lexer', 'BASIC_LEXER');
CTX_DDL.set_attribute ('mito_lexer', 'INDEX_STEMS', 'ITALIAN');
-- MITO-318: search on Text Index for Asterisks
CTX_DDL.set_attribute ('mito_lexer', 'printjoins', '*');
END;
/

Because the exclamation mark ("!") is a reserved operator, meaning soundex, and must appear before the word it applies to.

Why MATLAB Language Syntax Return Error 1048?

Why Does My Script Written in The MathWorks, Inc. MATLAB® Language Syntax Return Error 1048?
x = (0:0.1:10)';
y = sin(2*x)./exp(x/5);
trnData = [x y];
numMFs = 5;
mfType = 'gbellmf';
epoch_n = 20;
in_fis = genfis1(trnData,numMFs,mfType);
out_fis = anfis(trnData,in_fis,20);
aa = evalfis([x x1],out_fis);
http://www.mathworks.com/help/fuzzy/anfis.html

What do you get if you define the output as a 2D array?
(Or transpose the vector. Remember that matlab has a distinction between row and column vectors and LabVIEW does not). If you create a 2D array, it can be 1xN or Nx1 and you get all elements either way.)
LabVIEW Champion . Do more with less code and in less time .

Object Query Language (OQL) Support ?

I know Toplink has an "ExpressionBuilder" type querying
But does Toplink support Object Query Language (OQL)
Example :
Something like this ?
// perform query
OQLQuery query = new OQLQuery(
"select x from Person x where x.name = \"Doug Barry\"");
Collection result = (Collection) query.execute();
Iterator iter = result.iterator();
Thanks
Ratheesh

Ratheesh,
TopLink does not support OQL. We offer query support through the following 5 options:
1. EJB QL - for both Entity Beans (CMP/BMP) and Java objects
2. TopLink Expressions - Object based query API
3. SQL calls
4. Stored procedure calls
5. Quey by example
Doug

JPA query language syntax

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