Hi friends, can anyone please help me in this topic. I searched the EJB spec for this.but did not find the answer. I know that we write EJB-QL queries in ejb-ql tag in DD,But where is it located? So how the container looks for information in finder methods of home interface and select methods bean class when it comes across a ELB-QL query?
I have taken this reference from EJB cookbook, which may help you to understand the things.
Let�s examine a query method description from the deployment descriptor more closely:
Each custom finder method should be described by a <query/> block in the deployment descriptor for each bean. In the <query/> tag, you specify the method name and its parameter types (in the order that they appear in the method). Lastly, you specify the EJB-QL string that represents the entity bean query that the method should execute to return an entity bean or beans to the EJB client. An EJB-QL string resembles a JDBC prepared statement in that arguments are represented by a question mark (?). However, in EJB-QL you also add a number next to the ? that specifies which argument it represents (first, second, third, and so forth). EJB-QL is not hard to use, but it also does not encompass as many features as SQL. Examining our statements, you can see they have three parts:
1.The SELECT clause can return any EJB object, CMP, or CMR field. When returning an EJB, the statement must use the OBJECT() operator to surround the return type. If returning a field, you can simply state the field, like SELECT a.symbol. In the SELECT part, you can also make use of the DISTINCT keyword, as in SELECT DISTINCT OBJECT(a). This will cause each returned value to be unique, with no duplicates.
2.The FROM clause allows you to select the scope to pull data from. For instance, in our queries we are extracting data from the EquityBean EJBs. The AS keyword lets you rename the bean with an identifier. The identifier cannot be a name that is already used for an EJB name or abstract schema name (and the identifier is not case sensitive).
3. The WHERE clause lets you drill down to specific data by setting up conditions. The data returned from the statement must meet the conditions in this clause. In our example, the lastTrade field of an EquityBean EJB should be greater than our input parameter. For more information on EJB-QL, go to Here
Hope, it helps
[ March 29, 2006: Message edited by: Mishra Anshu ] [ March 29, 2006: Message edited by: Mishra Anshu ]
"Ignorance is bliss"
posted 14 years ago
Hi Mishra Anshu Thank you very very much for your prompt reply and detailed explanation. Now I understood the concept thoroughly.