Hello everyone,
I've been trying to use OJB lately but I'm a newbie and I'm stuck with
handling simple non decomposed M:N relationships.
Here's my purpose :
A <- m:n -> B
A <- m:n -> C
*** Mapping is :
<class-descriptor class="my.test.business.A"
table="TBLA">
<field-descriptor name="id" column="ID" jdbc-type="BIGINT"
nullable="false" indexed="true" primarykey="true"
autoincrement="true">
</field-descriptor>
<field-descriptor name="att1" column="ATT1" jdbc-type="BIGINT"
nullable="false" indexed="true">
</field-descriptor>
<field-descriptor name="att2" column="ATT2" jdbc-type="VARCHAR"
nullable="true" indexed="false">
</field-descriptor>
<collection-descriptor name="bs"
collection-class="org.apache.ojb.broker.util.collections.ManageableArrayList"
element-class="my.test.business.B"
auto-retrieve="false" auto-update="link"
indirection-table="TBLAB">
<fk-pointing-to-this-class column="A_ID" />
<fk-pointing-to-element-class column="B_ID" />
</collection-descriptor>
<collection-descriptor name="cs"
collection-class="org.apache.ojb.broker.util.collections.ManageableArrayList"
element-class="my.test.business.C"
auto-retrieve="false" auto-update="link"
indirection-table="TBLAC">
<fk-pointing-to-this-class column="A_ID" />
<fk-pointing-to-element-class column="C_ID" />
</collection-descriptor>
</class-descriptor>
<class-descriptor class="my.test.business.B"
table="TBLB">
<field-descriptor name="id" column="ID" jdbc-type="BIGINT"
nullable="false" indexed="true" primarykey="true"
autoincrement="true">
</field-descriptor>
<field-descriptor name="label" column="LABEL"
jdbc-type="VARCHAR" nullable="false" indexed="false">
</field-descriptor>
<collection-descriptor name="as"
collection-class="org.apache.ojb.broker.util.collections.ManageableArrayList"
element-class="my.test.business.A"
auto-retrieve="false" auto-update="link"
indirection-table="TBLAB">
<fk-pointing-to-this-class column="B_ID" />
<fk-pointing-to-element-class column="A_ID" />
</collection-descriptor>
</class-descriptor>
<class-descriptor class="my.test.business.C"
table="TBLC">
<field-descriptor name="id" column="ID" jdbc-type="BIGINT"
nullable="false" indexed="true" primarykey="true"
autoincrement="true">
</field-descriptor>
<field-descriptor name="label" column="LABEL"
jdbc-type="VARCHAR" nullable="false" indexed="false">
</field-descriptor>
<collection-descriptor name="as"
collection-class="org.apache.ojb.broker.util.collections.ManageableArrayList"
element-class="my.test.business.A"
auto-retrieve="false" auto-update="link"
indirection-table="TBLAC">
<fk-pointing-to-this-class column="C_ID" />
<fk-pointing-to-element-class column="A_ID" />
</collection-descriptor>
</class-descriptor>
*** DDL is :
CREATE TABLE SEQ (
TABLENAME varchar(250) NOT NULL,
MAX_KEY bigint(20) default NULL,
GRAB_SIZE int(11) default NULL,
VERSION int(11) default NULL,
PRIMARY KEY (TABLENAME)
)
CREATE TABLE TBLA (
ID bigint(20) unsigned NOT NULL auto_increment,
ATT1 bigint(20) unsigned NOT NULL default '0',
ATT2 varchar(255) default NULL,
PRIMARY KEY (ID)
)
CREATE TABLE TBLB (
ID bigint(20) unsigned NOT NULL auto_increment,
LABEL varchar(255) default NULL,
PRIMARY KEY (ID)
)
CREATE TABLE TBLC (
ID bigint(20) unsigned NOT NULL auto_increment,
LABEL varchar(255) default NULL,
PRIMARY KEY (ID)
)
CREATE TABLE TBLAB (
A_ID bigint(20) unsigned NOT NULL default '0',
B_ID bigint(20) unsigned NOT NULL default '0',
PRIMARY KEY (A_ID,B_ID),
CONSTRAINT FKAB1 FOREIGN KEY (A_ID) REFERENCES A (ID),
CONSTRAINT FKAB2 FOREIGN KEY (B_ID) REFERENCES B (ID)
)
CREATE TABLE TBLAC (
A_ID bigint(20) unsigned NOT NULL default '0',
C_ID bigint(20) unsigned NOT NULL default '0',
PRIMARY KEY (A_ID,C_ID),
CONSTRAINT FKAC1 FOREIGN KEY (A_ID) REFERENCES A (ID),
CONSTRAINT FKAC2 FOREIGN KEY (C_ID) REFERENCES C (ID)
)
*** and code is :
public class A implements Serializable {
private Long id;
private Long att1;
private String att2;
private List bs = new ArrayList();
private List cs = new ArrayList();
/* and getters/setters */
}
public class B implements Serializable {
private Long id;
private String label;
private List as = new ArrayList();
/* and getters/setters */
}
public class C implements Serializable {
private Long id;
private String label;
private List as = new ArrayList();
/* and getters/setters */
}
***
You might have noticed the collections auto-retrieve setting is set to
'false'. If I set this setting to true in *A* class mapping, I get a
NullPointerException when I try to read instances of A.
Furthermore, auto-retrieve set to false, I can read and add new objects
but I also get NullPointerExceptions when trying to update an object
already stored.
Is there anything I'm doing wrong ? Please, do not hesitate to ask me
questions. Any help would be greatly appreciated.
Many thanks.
Ramzi Oueslati
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