EJB-QL and date/time types

Question

Hi,
as far as I understand, EJB-QL does not support date/time values.
Does anybody know how to work around this limitation?
Using long values containing milliseconds is not an alternative, because the database stores
date/time values.
I need to compare these date/time values to input parameters in finder methods.
Suggestions?
Bye the way, is there any reason for this limitation in EJB-QL, or did they simply forget to include
date/time types to the spec?
Greetings
Christian

Answer 1

Greetings,
Hi,
as far as I understand, EJB-QL does not support
date/time values. Actually, it does - EJB QL supports all types supported by a bean's abstract schema (IOW: available types for CMP/CMR fields). However, therein also lies the crutch - EJB QL is for querying beans, not the resource to which they map (EJB QL's similarity to SQL is purely for convenience; an Entity Bean, it should be remembered, may represent entities in any persistent store, not just RDBMSes). Therefore, you should be thinking in terms of Java types, not SQL ones... The specification, however, does place "restrictions" (ie. minimally required [vendor] support), on their use which should be limited to long millisecond values (by which a Date object performs an equals comparison... ;).
Does anybody know how to work around this limitation?Depends on what you're attempting. If you're using a Date as an argument to a finder, eg:
findByDateInRange( java.util.Date start, java.util.Date end )then this shouldn't pose a problem where your EJB QL would look like:
SELECT OBJECT(a) FROM MyBeanSchema AS a WHERE a.myDate BETWEEN ?1 AND ?2Presuming the bean MyBean contains a CMP field of type java.util.Date called 'myDate'. If, however, you must use a literal date then you will have to use a long literal unless your vendor supports otherwise. However, it might be worth noting that EJB QL must still be mapped to the underlying resource QL (eg. SQL), and so a more intelligble value (one that meets the resource's format requirements ;), could be used in the actual rQL statement.
Using long values containing milliseconds is not an
alternative, because the database stores
date/time values.I'm guessing you mean here something like "04/23/2002" and "13:13:35", etc. This, however, is not how the database actually stores the data - input/output formats such as these are supported for the convenience of us 'nuerically-challenged' humans (similar to internet hostnames vs. TCP/IP addresses ;) - nor do Java Date/Calendar/Timestamp types store them this way.
I need to compare these date/time values to input
parameters in finder methods.
Suggestions?Ah, yes. Well then... refer back to the above. :)
Bye the way, is there any reason for this limitation
in EJB-QL, or did they simply forget to include
date/time types to the spec?The EJB QL does not explicitly support any specific types beyond those "supported by an EJB's abstract schema", which is pretty much any Java type that can represent a compatible resource type. The reason for the noted "restriction" on date/time types, however, is (likely) due to the way the associated Java classes (not to mention the back-end resource), handle/represent these data internally and this gives the vendor an easily achievable minimal level of compliance for supporting these types.
I hope this helps.
ChristianRegards,
Tony "Vee Schade" Cook