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25  
26  package javax.sql.rowset;
27  
28  import java.sql.SQLException;
29  
30  /**
31   * <h3>1.0 Background</h3>
32   * The <code>Joinable</code> interface provides the methods for getting and
33   * setting a match column, which is the basis for forming the SQL <code>JOIN</code>
34   * formed by adding <code>RowSet</code> objects to a <code>JoinRowSet</code>
35   * object.
36   * <P>
37   * Any standard <code>RowSet</code> implementation <b>may</b> implement
38   * the <code>Joinable</code> interface in order to be
39   * added to a <code>JoinRowSet</code> object. Implementing this interface gives
40   * a <code>RowSet</code> object the ability to use <code>Joinable</code> methods,
41   * which set, retrieve, and get information about match columns.  An
42   * application may add a
43   * <code>RowSet</code> object that has not implemented the <code>Joinable</code>
44   * interface to a <code>JoinRowSet</code> object, but to do so it must use one
45   * of the <code>JoinRowSet.addRowSet</code> methods that takes both a
46   * <code>RowSet</code> object and a match column or an array of <code>RowSet</code>
47   * objects and an array of match columns.
48   * <P>
49   * To get access to the methods in the <code>Joinable</code> interface, a
50   * <code>RowSet</code> object implements at least one of the
51   * five standard <code>RowSet</code> interfaces and also implements the
52   * <code>Joinable</code> interface.  In addition, most <code>RowSet</code>
53   * objects extend the <code>BaseRowSet</code> class.  For example:
54   * <pre>
55   *     class MyRowSetImpl extends BaseRowSet implements CachedRowSet, Joinable {
56   *         :
57   *         :
58   *     }
59   * </pre>
60   *
61   * <h3>2.0 Usage Guidelines</h3>
62   * <P>
63   * The methods in the <code>Joinable</code> interface allow a <code>RowSet</code> object
64   * to set a match column, retrieve a match column, or unset a match column, which is
65   * the column upon which an SQL <code>JOIN</code> can be based.
66   * An instance of a class that implements these methods can be added to a
67   * <code>JoinRowSet</code> object to allow an SQL <code>JOIN</code> relationship to
68   *  be established.
69   *
70   * <pre>
71   *     CachedRowSet crs = new MyRowSetImpl();
72   *     crs.populate((ResultSet)rs);
73   *     (Joinable)crs.setMatchColumnIndex(1);
74   *
75   *     JoinRowSet jrs = new JoinRowSetImpl();
76   *     jrs.addRowSet(crs);
77   * </pre>
78   * In the previous example, <i>crs</i> is a <code>CachedRowSet</code> object that
79   * has implemented the <code>Joinable</code> interface.  In the following example,
80   * <i>crs2</i> has not, so it must supply the match column as an argument to the
81   * <code>addRowSet</code> method. This example assumes that column 1 is the match
82   * column.
83   * <PRE>
84   *     CachedRowSet crs2 = new MyRowSetImpl();
85   *     crs2.populate((ResultSet)rs);
86   *
87   *     JoinRowSet jrs2 = new JoinRowSetImpl();
88   *     jrs2.addRowSet(crs2, 1);
89   * </PRE>
90   * <p>
91   * The <code>JoinRowSet</code> interface makes it possible to get data from one or
92   * more <code>RowSet</code> objects consolidated into one table without having to incur
93   * the expense of creating a connection to a database. It is therefore ideally suited
94   * for use by disconnected <code>RowSet</code> objects. Nevertheless, any
95   * <code>RowSet</code> object <b>may</b> implement this interface
96   * regardless of whether it is connected or disconnected. Note that a
97   * <code>JdbcRowSet</code> object, being always connected to its data source, can
98   * become part of an SQL <code>JOIN</code> directly without having to become part
99   * of a <code>JoinRowSet</code> object.
100  *
101  * <h3>3.0 Managing Multiple Match Columns</h3>
102  * The index array passed into the <code>setMatchColumn</code> methods indicates
103  * how many match columns are being set (the length of the array) in addition to
104  * which columns will be used for the match. For example:
105  * <pre>
106  *     int[] i = {1, 2, 4, 7}; // indicates four match columns, with column
107  *                             // indexes 1, 2, 4, 7 participating in the JOIN.
108  *     Joinable.setMatchColumn(i);
109  * </pre>
110  * Subsequent match columns may be added as follows to a different <code>Joinable</code>
111  * object (a <code>RowSet</code> object that has implemented the <code>Joinable</code>
112  * interface).
113  * <pre>
114  *     int[] w = {3, 2, 5, 3};
115  *     Joinable2.setMatchColumn(w);
116  * </pre>
117  * When an application adds two or more <code>RowSet</code> objects to a
118  * <code>JoinRowSet</code> object, the order of the indexes in the array is
119  * particularly important. Each index of
120  * the array maps directly to the corresponding index of the previously added
121  * <code>RowSet</code> object. If overlap or underlap occurs, the match column
122  * data is maintained in the event an additional <code>Joinable</code> RowSet is
123  * added and needs to relate to the match column data. Therefore, applications
124  * can set multiple match columns in any order, but
125  * this order has a direct effect on the outcome of the <code>SQL</code> JOIN.
126  * <p>
127  * This assertion applies in exactly the same manner when column names are used
128  * rather than column indexes to indicate match columns.
129  *
130  * @see JoinRowSet
131  * @author  Jonathan Bruce
132  */
133 public interface Joinable {
134 
135     /**
136      * Sets the designated column as the match column for this <code>RowSet</code>
137      * object. A <code>JoinRowSet</code> object can now add this <code>RowSet</code>
138      * object based on the match column.
139      * <p>
140      * Sub-interfaces such as the <code>CachedRowSet</code>&trade;
141      * interface define the method <code>CachedRowSet.setKeyColumns</code>, which allows
142      * primary key semantics to be enforced on specific columns.
143      * Implementations of the <code>setMatchColumn(int columnIdx)</code> method
144      * should ensure that the constraints on the key columns are maintained when
145      * a <code>CachedRowSet</code> object sets a primary key column as a match column.
146      *
147      * @param columnIdx an <code>int</code> identifying the index of the column to be
148      *        set as the match column
149      * @throws SQLException if an invalid column index is set
150      * @see #setMatchColumn(int[])
151      * @see #unsetMatchColumn(int)
152      *
153      */
154     public void setMatchColumn(int columnIdx) throws SQLException;
155 
156     /**
157      * Sets the designated columns as the match column for this <code>RowSet</code>
158      * object. A <code>JoinRowSet</code> object can now add this <code>RowSet</code>
159      * object based on the match column.
160      *
161      * @param columnIdxes an array of <code>int</code> identifying the indexes of the
162      *      columns to be set as the match columns
163      * @throws SQLException if an invalid column index is set
164      * @see #setMatchColumn(int[])
165      * @see #unsetMatchColumn(int[])
166      */
167     public void setMatchColumn(int[] columnIdxes) throws SQLException;
168 
169     /**
170      * Sets the designated column as the match column for this <code>RowSet</code>
171      * object. A <code>JoinRowSet</code> object can now add this <code>RowSet</code>
172      * object based on the match column.
173      * <p>
174      * Subinterfaces such as the <code>CachedRowSet</code> interface define
175      * the method <code>CachedRowSet.setKeyColumns</code>, which allows
176      * primary key semantics to be enforced on specific columns.
177      * Implementations of the <code>setMatchColumn(String columnIdx)</code> method
178      * should ensure that the constraints on the key columns are maintained when
179      * a <code>CachedRowSet</code> object sets a primary key column as a match column.
180      *
181      * @param columnName a <code>String</code> object giving the name of the column
182      *      to be set as the match column
183      * @throws SQLException if an invalid column name is set, the column name
184      *      is a null, or the column name is an empty string
185      * @see #unsetMatchColumn
186      * @see #setMatchColumn(int[])
187      */
188     public void setMatchColumn(String columnName) throws SQLException;
189 
190     /**
191      * Sets the designated columns as the match column for this <code>RowSet</code>
192      * object. A <code>JoinRowSet</code> object can now add this <code>RowSet</code>
193      * object based on the match column.
194      *
195      * @param columnNames an array of <code>String</code> objects giving the names
196      *     of the column to be set as the match columns
197      * @throws SQLException if an invalid column name is set, the column name
198      *      is a null, or the column name is an empty string
199      * @see #unsetMatchColumn
200      * @see #setMatchColumn(int[])
201      */
202     public void setMatchColumn(String[] columnNames) throws SQLException;
203 
204     /**
205      * Retrieves the indexes of the match columns that were set for this
206      * <code>RowSet</code> object with the method
207      * <code>setMatchColumn(int[] columnIdxes)</code>.
208      *
209      * @return an <code>int</code> array identifying the indexes of the columns
210      *         that were set as the match columns for this <code>RowSet</code> object
211      * @throws SQLException if no match column has been set
212      * @see #setMatchColumn
213      * @see #unsetMatchColumn
214      */
215     public int[] getMatchColumnIndexes() throws SQLException;
216 
217     /**
218      * Retrieves the names of the match columns that were set for this
219      * <code>RowSet</code> object with the method
220      * <code>setMatchColumn(String [] columnNames)</code>.
221      *
222      * @return an array of <code>String</code> objects giving the names of the columns
223      *         set as the match columns for this <code>RowSet</code> object
224      * @throws SQLException if no match column has been set
225      * @see #setMatchColumn
226      * @see #unsetMatchColumn
227      *
228      */
229     public String[] getMatchColumnNames() throws SQLException;
230 
231     /**
232      * Unsets the designated column as the match column for this <code>RowSet</code>
233      * object.
234      * <P>
235      * <code>RowSet</code> objects that implement the <code>Joinable</code> interface
236      * must ensure that a key-like constraint continues to be enforced until the
237      * method <code>CachedRowSet.unsetKeyColumns</code> has been called on the
238      * designated column.
239      *
240      * @param columnIdx an <code>int</code> that identifies the index of the column
241      *          that is to be unset as a match column
242      * @throws SQLException if an invalid column index is designated or if
243      *          the designated column was not previously set as a match
244      *          column
245      * @see #setMatchColumn
246      */
247     public void unsetMatchColumn(int columnIdx) throws SQLException;
248 
249     /**
250      * Unsets the designated columns as the match column for this <code>RowSet</code>
251      * object.
252      *
253      * @param columnIdxes an array of <code>int</code> that identifies the indexes
254      *     of the columns that are to be unset as match columns
255      * @throws SQLException if an invalid column index is designated or if
256      *          the designated column was not previously set as a match
257      *          column
258      * @see #setMatchColumn
259      */
260     public void unsetMatchColumn(int[] columnIdxes) throws SQLException;
261 
262     /**
263      * Unsets the designated column as the match column for this <code>RowSet</code>
264      * object.
265      * <P>
266      * <code>RowSet</code> objects that implement the <code>Joinable</code> interface
267      * must ensure that a key-like constraint continues to be enforced until the
268      * method <code>CachedRowSet.unsetKeyColumns</code> has been called on the
269      * designated column.
270      *
271      * @param columnName a <code>String</code> object giving the name of the column
272      *          that is to be unset as a match column
273      * @throws SQLException if an invalid column name is designated or
274      *          the designated column was not previously set as a match
275      *          column
276      * @see #setMatchColumn
277      */
278     public void unsetMatchColumn(String columnName) throws SQLException;
279 
280     /**
281      * Unsets the designated columns as the match columns for this <code>RowSet</code>
282      * object.
283      *
284      * @param columnName an array of <code>String</code> objects giving the names of
285      *     the columns that are to be unset as the match columns
286      * @throws SQLException if an invalid column name is designated or the
287      *     designated column was not previously set as a match column
288      * @see #setMatchColumn
289      */
290     public void unsetMatchColumn(String[] columnName) throws SQLException;
291 }