javax.sql.rowset.JoinRowSet
The JoinRowSet interface provides a mechanism for combining related data from different RowSet objects into one JoinRowSet object, which represents an SQL JOIN. In other words, a JoinRowSet object acts as a container for the data from RowSet objects that form an SQL JOIN relationship.
The Joinable interface provides the methods for setting, retrieving, and unsetting a match column, the basis for establishing an SQL JOIN relationship. The match column may alternatively be set by supplying it to the appropriate version of the JointRowSet method addRowSet.
1.0 Overview Disconnected RowSet objects (CachedRowSet objects and implementations extending the CachedRowSet interface) do not have a standard way to establish an SQL JOIN between RowSet objects without the expensive operation of reconnecting to the data source. The JoinRowSet interface is specifically designed to address this need.
Any RowSet object can be added to a JoinRowSet object to become part of an SQL JOIN relationship. This means that both connected and disconnected RowSet objects can be part of a JOIN. RowSet objects operating in a connected environment (JdbcRowSet objects) are encouraged to use the database to which they are already connected to establish SQL JOIN relationships between tables directly. However, it is possible for a JdbcRowSet object to be added to a JoinRowSet object if necessary.
Any number of RowSet objects can be added to an instance of JoinRowSet provided that they can be related in an SQL JOIN. By definition, the SQL JOIN statement is used to combine the data contained in two or more relational database tables based upon a common attribute. The Joinable interface provides the methods for establishing a common attribute, which is done by setting a match column. The match column commonly coincides with the primary key, but there is no requirement that the match column be the same as the primary key. By establishing and then enforcing column matches, a JoinRowSet object establishes JOIN relationships between RowSet objects without the assistance of an available relational database.
The type of JOIN to be established is determined by setting one of the JoinRowSet constants using the method setJoinType. The following SQL JOIN types can be set:
CROSS_JOIN FULL_JOIN INNER_JOIN - the default if no JOIN type has been set LEFT_OUTER_JOIN RIGHT_OUTER_JOIN
Note that if no type is set, the JOIN will automatically be an inner join. The comments for the fields in the JoinRowSet interface explain these JOIN types, which are standard SQL JOIN types.
2.0 Using a JoinRowSet Object for Creating a JOIN When a JoinRowSet object is created, it is empty. The first RowSet object to be added becomes the basis for the JOIN relationship. Applications must determine which column in each of the RowSet objects to be added to the JoinRowSet object should be the match column. All of the RowSet objects must contain a match column, and the values in each match column must be ones that can be compared to values in the other match columns. The columns do not have to have the same name, though they often do, and they do not have to store the exact same data type as long as the data types can be compared.
A match column can be be set in two ways:
By calling the Joinable method setMatchColumn This is the only method that can set the match column before a RowSet object is added to a JoinRowSet object. The RowSet object must have implemented the Joinable interface in order to use the method setMatchColumn. Once the match column value has been set, this method can be used to reset the match column at any time. By calling one of the versions of the JoinRowSet method addRowSet that takes a column name or number (or an array of column names or numbers) Four of the five addRowSet methods take a match column as a parameter. These four methods set or reset the match column at the time a RowSet object is being added to a JoinRowSet object.
3.0 Sample Usage
The following code fragment adds two CachedRowSet objects to a JoinRowSet object. Note that in this example, no SQL JOIN type is set, so the default JOIN type, which is INNER_JOIN, is established.
In the following code fragment, the table EMPLOYEES, whose match column is set to the first column (EMP_ID), is added to the JoinRowSet object jrs. Then the table ESSP_BONUS_PLAN, whose match column is likewise the EMP_ID column, is added. When this second table is added to jrs, only the rows in ESSP_BONUS_PLAN whose EMP_ID value matches an EMP_ID value in the EMPLOYEES table are added. In this case, everyone in the bonus plan is an employee, so all of the rows in the table ESSP_BONUS_PLAN are added to the JoinRowSet object. In this example, both CachedRowSet objects being added have implemented the Joinable interface and can therefore call the Joinable method setMatchColumn.
JoinRowSet jrs = new JoinRowSetImpl();
ResultSet rs1 = stmt.executeQuery(`SELECT * FROM EMPLOYEES`);
CachedRowSet empl = new CachedRowSetImpl();
empl.populate(rs1);
empl.setMatchColumn(1);
jrs.addRowSet(empl);
ResultSet rs2 = stmt.executeQuery(`SELECT * FROM ESSP_BONUS_PLAN`);
CachedRowSet bonus = new CachedRowSetImpl();
bonus.populate(rs2);
bonus.setMatchColumn(1); // EMP_ID is the first column
jrs.addRowSet(bonus);
At this point, jrs is an inside JOIN of the two RowSet objects based on their EMP_ID columns. The application can now browse the combined data as if it were browsing one single RowSet object. Because jrs is itself a RowSet object, an application can navigate or modify it using RowSet methods.
jrs.first();
int employeeID = jrs.getInt(1);
String employeeName = jrs.getString(2);
Note that because the SQL JOIN must be enforced when an application adds a second or subsequent RowSet object, there may be an initial degradation in performance while the JOIN is being performed.
The following code fragment adds an additional CachedRowSet object. In this case, the match column (EMP_ID) is set when the CachedRowSet object is added to the JoinRowSet object.
ResultSet rs3 = stmt.executeQuery(`SELECT * FROM 401K_CONTRIB`);
CachedRowSet fourO1k = new CachedRowSetImpl();
four01k.populate(rs3);
jrs.addRowSet(four01k, 1);
The JoinRowSet object jrs now contains values from all three tables. The data in each row in four01k in which the value for the EMP_ID column matches a value for the EMP_ID column in jrs has been added to jrs.
4.0 JoinRowSet Methods The JoinRowSet interface supplies several methods for adding RowSet objects and for getting information about the JoinRowSet object.
Methods for adding one or more RowSet objects These methods allow an application to add one RowSet object at a time or to add multiple RowSet objects at one time. In either case, the methods may specify the match column for each RowSet object being added. Methods for getting information One method retrieves the RowSet objects in the JoinRowSet object, and another method retrieves the RowSet names. A third method retrieves either the SQL WHERE clause used behind the scenes to form the JOIN or a text description of what the WHERE clause does. Methods related to the type of JOIN One method sets the JOIN type, and five methods find out whether the JoinRowSet object supports a given type. A method to make a separate copy of the JoinRowSet object This method creates a copy that can be persisted to the data source.
The JoinRowSet interface provides a mechanism for combining related
data from different RowSet objects into one JoinRowSet
object, which represents an SQL JOIN.
In other words, a JoinRowSet object acts as a
container for the data from RowSet objects that form an SQL
JOIN relationship.
The Joinable interface provides the methods for setting,
retrieving, and unsetting a match column, the basis for
establishing an SQL JOIN relationship. The match column may
alternatively be set by supplying it to the appropriate version of the
JointRowSet method addRowSet.
1.0 Overview
Disconnected RowSet objects (CachedRowSet objects
and implementations extending the CachedRowSet interface)
do not have a standard way to establish an SQL JOIN between
RowSet objects without the expensive operation of
reconnecting to the data source. The JoinRowSet
interface is specifically designed to address this need.
Any RowSet object
can be added to a JoinRowSet object to become
part of an SQL JOIN relationship. This means that both connected
and disconnected RowSet objects can be part of a JOIN.
RowSet objects operating in a connected environment
(JdbcRowSet objects) are
encouraged to use the database to which they are already
connected to establish SQL JOIN relationships between
tables directly. However, it is possible for a
JdbcRowSet object to be added to a JoinRowSet object
if necessary.
Any number of RowSet objects can be added to an
instance of JoinRowSet provided that they
can be related in an SQL JOIN.
By definition, the SQL JOIN statement is used to
combine the data contained in two or more relational database tables based
upon a common attribute. The Joinable interface provides the methods
for establishing a common attribute, which is done by setting a
match column. The match column commonly coincides with
the primary key, but there is
no requirement that the match column be the same as the primary key.
By establishing and then enforcing column matches,
a JoinRowSet object establishes JOIN relationships
between RowSet objects without the assistance of an available
relational database.
The type of JOIN to be established is determined by setting
one of the JoinRowSet constants using the method
setJoinType. The following SQL JOIN types can be set:
CROSS_JOIN
FULL_JOIN
INNER_JOIN - the default if no JOIN type has been set
LEFT_OUTER_JOIN
RIGHT_OUTER_JOIN
Note that if no type is set, the JOIN will automatically be an
inner join. The comments for the fields in the
JoinRowSet interface explain these JOIN types, which are
standard SQL JOIN types.
2.0 Using a JoinRowSet Object for Creating a JOIN
When a JoinRowSet object is created, it is empty.
The first RowSet object to be added becomes the basis for the
JOIN relationship.
Applications must determine which column in each of the
RowSet objects to be added to the JoinRowSet object
should be the match column. All of the
RowSet objects must contain a match column, and the values in
each match column must be ones that can be compared to values in the other match
columns. The columns do not have to have the same name, though they often do,
and they do not have to store the exact same data type as long as the data types
can be compared.
A match column can be be set in two ways:
By calling the Joinable method setMatchColumn
This is the only method that can set the match column before a RowSet
object is added to a JoinRowSet object. The RowSet object
must have implemented the Joinable interface in order to use the method
setMatchColumn. Once the match column value
has been set, this method can be used to reset the match column at any time.
By calling one of the versions of the JoinRowSet method
addRowSet that takes a column name or number (or an array of
column names or numbers)
Four of the five addRowSet methods take a match column as a parameter.
These four methods set or reset the match column at the time a RowSet
object is being added to a JoinRowSet object.
3.0 Sample Usage
The following code fragment adds two CachedRowSet
objects to a JoinRowSet object. Note that in this example,
no SQL JOIN type is set, so the default JOIN type,
which is INNER_JOIN, is established.
In the following code fragment, the table EMPLOYEES, whose match
column is set to the first column (EMP_ID), is added to the
JoinRowSet object jrs. Then
the table ESSP_BONUS_PLAN, whose match column is likewise
the EMP_ID column, is added. When this second
table is added to jrs, only the rows in
ESSP_BONUS_PLAN whose EMP_ID value matches an
EMP_ID value in the EMPLOYEES table are added.
In this case, everyone in the bonus plan is an employee, so all of the rows
in the table ESSP_BONUS_PLAN are added to the JoinRowSet
object. In this example, both CachedRowSet objects being added
have implemented the Joinable interface and can therefore call
the Joinable method setMatchColumn.
JoinRowSet jrs = new JoinRowSetImpl();
ResultSet rs1 = stmt.executeQuery(`SELECT * FROM EMPLOYEES`);
CachedRowSet empl = new CachedRowSetImpl();
empl.populate(rs1);
empl.setMatchColumn(1);
jrs.addRowSet(empl);
ResultSet rs2 = stmt.executeQuery(`SELECT * FROM ESSP_BONUS_PLAN`);
CachedRowSet bonus = new CachedRowSetImpl();
bonus.populate(rs2);
bonus.setMatchColumn(1); // EMP_ID is the first column
jrs.addRowSet(bonus);
At this point, jrs is an inside JOIN of the two RowSet objects
based on their EMP_ID columns. The application can now browse the
combined data as if it were browsing one single RowSet object.
Because jrs is itself a RowSet object, an application can
navigate or modify it using RowSet methods.
jrs.first();
int employeeID = jrs.getInt(1);
String employeeName = jrs.getString(2);
Note that because the SQL JOIN must be enforced when an application
adds a second or subsequent RowSet object, there
may be an initial degradation in performance while the JOIN is
being performed.
The following code fragment adds an additional CachedRowSet object.
In this case, the match column (EMP_ID) is set when the
CachedRowSet object is added to the JoinRowSet object.
ResultSet rs3 = stmt.executeQuery(`SELECT * FROM 401K_CONTRIB`);
CachedRowSet fourO1k = new CachedRowSetImpl();
four01k.populate(rs3);
jrs.addRowSet(four01k, 1);
The JoinRowSet object jrs now contains values from all three
tables. The data in each row in four01k in which the value for the
EMP_ID column matches a value for the EMP_ID column
in jrs has been added to jrs.
4.0 JoinRowSet Methods
The JoinRowSet interface supplies several methods for adding
RowSet objects and for getting information about the
JoinRowSet object.
Methods for adding one or more RowSet objects
These methods allow an application to add one RowSet object
at a time or to add multiple RowSet objects at one time. In
either case, the methods may specify the match column for each
RowSet object being added.
Methods for getting information
One method retrieves the RowSet objects in the
JoinRowSet object, and another method retrieves the
RowSet names. A third method retrieves either the SQL
WHERE clause used behind the scenes to form the
JOIN or a text description of what the WHERE
clause does.
Methods related to the type of JOIN
One method sets the JOIN type, and five methods find out whether
the JoinRowSet object supports a given type.
A method to make a separate copy of the JoinRowSet object
This method creates a copy that can be persisted to the data source.add-row-setclj
(add-row-set this rowset)(add-row-set this rowset column-idx)Adds the given RowSet object to this JoinRowSet object and sets the designated column as the match column for the RowSet object. If the RowSet object is the first to be added to this JoinRowSet object, it forms the basis of the JOIN relationship to be established.
This method should be used when RowSet does not already have a match column set.
rowset - the RowSet object that is to be added to this JoinRowSet object; it may implement the Joinable interface - javax.sql.RowSet
column-idx - an int that identifies the column to become the match column - int
throws: java.sql.SQLException - if (1) rowset is an empty rowset or (2) rowset violates the active JOIN
Adds the given RowSet object to this JoinRowSet object and sets the designated column as the match column for the RowSet object. If the RowSet object is the first to be added to this JoinRowSet object, it forms the basis of the JOIN relationship to be established. This method should be used when RowSet does not already have a match column set. rowset - the RowSet object that is to be added to this JoinRowSet object; it may implement the Joinable interface - `javax.sql.RowSet` column-idx - an int that identifies the column to become the match column - `int` throws: java.sql.SQLException - if (1) rowset is an empty rowset or (2) rowset violates the active JOIN
get-join-typeclj
(get-join-type this)Returns a int describing the set SQL JOIN type governing this JoinRowSet instance. The returned type will be one of standard JoinRowSet types: CROSS_JOIN, INNER_JOIN, LEFT_OUTER_JOIN, RIGHT_OUTER_JOIN or FULL_JOIN.
returns: joinType one of the standard JoinRowSet static field
definitions of a SQL JOIN. JoinRowSet.INNER_JOIN
is returned as the default JOIN type is no type has been
explicitly set. - int
throws: java.sql.SQLException - if an error occurs determining the SQL JOIN type supported by the JoinRowSet instance.
Returns a int describing the set SQL JOIN type
governing this JoinRowSet instance. The returned type will be one of
standard JoinRowSet types: CROSS_JOIN, INNER_JOIN,
LEFT_OUTER_JOIN, RIGHT_OUTER_JOIN or
FULL_JOIN.
returns: joinType one of the standard JoinRowSet static field
definitions of a SQL JOIN. JoinRowSet.INNER_JOIN
is returned as the default JOIN type is no type has been
explicitly set. - `int`
throws: java.sql.SQLException - if an error occurs determining the SQL JOIN type supported by the JoinRowSet instance.get-row-set-namesclj
(get-row-set-names this)Returns a String array containing the names of the RowSet objects added to this JoinRowSet object.
returns: a String array of the names of the
RowSet objects in this JoinRowSet
object - java.lang.String[]
throws: java.sql.SQLException - if an error occurs retrieving the names of the RowSet objects
Returns a String array containing the names of the
RowSet objects added to this JoinRowSet
object.
returns: a String array of the names of the
RowSet objects in this JoinRowSet
object - `java.lang.String[]`
throws: java.sql.SQLException - if an error occurs retrieving the names of the RowSet objectsget-row-setsclj
(get-row-sets this)Returns a Collection object containing the RowSet objects that have been added to this JoinRowSet object. This should return the 'n' number of RowSet contained within the JOIN and maintain any updates that have occurred while in this union.
returns: a Collection object consisting of the
RowSet objects added to this JoinRowSet
object - java.util.Collection<?>
throws: java.sql.SQLException - if an error occurs generating the Collection object to be returned
Returns a Collection object containing the
RowSet objects that have been added to this
JoinRowSet object.
This should return the 'n' number of RowSet contained
within the JOIN and maintain any updates that have occurred while in
this union.
returns: a Collection object consisting of the
RowSet objects added to this JoinRowSet
object - `java.util.Collection<?>`
throws: java.sql.SQLException - if an error occurs generating the Collection object to be returnedget-where-clauseclj
(get-where-clause this)Return a SQL-like description of the WHERE clause being used in a JoinRowSet object. An implementation can describe the WHERE clause of the SQL JOIN by supplying a SQL strings description of JOIN or provide a textual description to assist applications using a JoinRowSet
returns: whereClause a textual or SQL description of the logical
WHERE clause used in the JoinRowSet instance - java.lang.String
throws: java.sql.SQLException - if an error occurs in generating a representation of the WHERE clause.
Return a SQL-like description of the WHERE clause being used in a JoinRowSet object. An implementation can describe the WHERE clause of the SQL JOIN by supplying a SQL strings description of JOIN or provide a textual description to assist applications using a JoinRowSet returns: whereClause a textual or SQL description of the logical WHERE clause used in the JoinRowSet instance - `java.lang.String` throws: java.sql.SQLException - if an error occurs in generating a representation of the WHERE clause.
set-join-typeclj
(set-join-type this join-type)Allow the application to adjust the type of JOIN imposed on tables contained within the JoinRowSet object instance. Implementations should throw a SQLException if they do not support a given JOIN type.
join-type - the standard JoinRowSet.XXX static field definition of a SQL JOIN to re-configure a JoinRowSet instance on the fly. - int
throws: java.sql.SQLException - if an unsupported JOIN type is set
Allow the application to adjust the type of JOIN imposed on tables contained within the JoinRowSet object instance. Implementations should throw a SQLException if they do not support a given JOIN type. join-type - the standard JoinRowSet.XXX static field definition of a SQL JOIN to re-configure a JoinRowSet instance on the fly. - `int` throws: java.sql.SQLException - if an unsupported JOIN type is set
supports-cross-joinclj
(supports-cross-join this)Indicates if CROSS_JOIN is supported by a JoinRowSet implementation
returns: true if the CROSS_JOIN is supported; false otherwise - boolean
Indicates if CROSS_JOIN is supported by a JoinRowSet implementation returns: true if the CROSS_JOIN is supported; false otherwise - `boolean`
supports-full-joinclj
(supports-full-join this)Indicates if FULL_JOIN is supported by a JoinRowSet implementation
returns: true is the FULL_JOIN is supported; false otherwise - boolean
Indicates if FULL_JOIN is supported by a JoinRowSet implementation returns: true is the FULL_JOIN is supported; false otherwise - `boolean`
supports-inner-joinclj
(supports-inner-join this)Indicates if INNER_JOIN is supported by a JoinRowSet implementation
returns: true is the INNER_JOIN is supported; false otherwise - boolean
Indicates if INNER_JOIN is supported by a JoinRowSet implementation returns: true is the INNER_JOIN is supported; false otherwise - `boolean`
supports-left-outer-joinclj
(supports-left-outer-join this)Indicates if LEFT_OUTER_JOIN is supported by a JoinRowSet implementation
returns: true is the LEFT_OUTER_JOIN is supported; false otherwise - boolean
Indicates if LEFT_OUTER_JOIN is supported by a JoinRowSet implementation returns: true is the LEFT_OUTER_JOIN is supported; false otherwise - `boolean`
supports-right-outer-joinclj
(supports-right-outer-join this)Indicates if RIGHT_OUTER_JOIN is supported by a JoinRowSet implementation
returns: true is the RIGHT_OUTER_JOIN is supported; false otherwise - boolean
Indicates if RIGHT_OUTER_JOIN is supported by a JoinRowSet implementation returns: true is the RIGHT_OUTER_JOIN is supported; false otherwise - `boolean`
to-cached-row-setclj
(to-cached-row-set this)Creates a new CachedRowSet object containing the data in this JoinRowSet object, which can be saved to a data source using the SyncProvider object for the CachedRowSet object.
If any updates or modifications have been applied to the JoinRowSet the CachedRowSet returned by the method will not be able to persist it's changes back to the originating rows and tables in the in the datasource. The CachedRowSet instance returned should not contain modification data and it should clear all properties of it's originating SQL statement. An application should reset the SQL statement using the RowSet.setCommand method.
In order to allow changes to be persisted back to the datasource to the originating tables, the acceptChanges method should be used and called on a JoinRowSet object instance. Implementations can leverage the internal data and update tracking in their implementations to interact with the SyncProvider to persist any changes.
returns: a CachedRowSet containing the contents of the JoinRowSet - javax.sql.rowset.CachedRowSet
throws: java.sql.SQLException - if an error occurs assembling the CachedRowSet object
Creates a new CachedRowSet object containing the data in this JoinRowSet object, which can be saved to a data source using the SyncProvider object for the CachedRowSet object. If any updates or modifications have been applied to the JoinRowSet the CachedRowSet returned by the method will not be able to persist it's changes back to the originating rows and tables in the in the datasource. The CachedRowSet instance returned should not contain modification data and it should clear all properties of it's originating SQL statement. An application should reset the SQL statement using the RowSet.setCommand method. In order to allow changes to be persisted back to the datasource to the originating tables, the acceptChanges method should be used and called on a JoinRowSet object instance. Implementations can leverage the internal data and update tracking in their implementations to interact with the SyncProvider to persist any changes. returns: a CachedRowSet containing the contents of the JoinRowSet - `javax.sql.rowset.CachedRowSet` throws: java.sql.SQLException - if an error occurs assembling the CachedRowSet object
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