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Java > Open Source Codes > org > objectstyle > cayenne > access > trans > OrderingTranslator


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2  *
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56 package org.objectstyle.cayenne.access.trans;
57
58 import java.util.ArrayList JavaDoc;
59 import java.util.List JavaDoc;
60
61 import org.objectstyle.cayenne.CayenneRuntimeException;
62 import org.objectstyle.cayenne.exp.Expression;
63 import org.objectstyle.cayenne.query.Ordering;
64 import org.objectstyle.cayenne.query.Query;
65 import org.objectstyle.cayenne.query.SelectQuery;
66
67 /**
68  * Translates query ordering to SQL.
69  *
70  * @author Andrei Adamchik
71  * @author Craig Miskell
72  */
73 public class OrderingTranslator extends QueryAssemblerHelper {
74
75     protected List JavaDoc orderByColumnList = new ArrayList JavaDoc();
76     
77     public OrderingTranslator(QueryAssembler queryAssembler) {
78         super(queryAssembler);
79     }
80
81     /** Translates query Ordering list to SQL ORDER BY clause.
82      * Ordering list is obtained from <code>queryAssembler</code>'s query object.
83      * In a process of building of ORDER BY clause, <code>queryAssembler</code>
84      * is notified when a join needs to be added. */
85     public String JavaDoc doTranslation() {
86         Query q = queryAssembler.getQuery();
87
88         // only select queries can have ordering...
89 if (q == null || !(q instanceof SelectQuery))
90             return null;
91
92         StringBuffer JavaDoc buf = new StringBuffer JavaDoc();
93         List JavaDoc list = ((SelectQuery) q).getOrderings();
94         int len = list.size();
95
96         for (int i = 0; i < len; i++) {
97             if (i > 0)
98                 buf.append(", ");
99
100             StringBuffer JavaDoc ordComp = new StringBuffer JavaDoc();
101
102             Ordering ord = (Ordering) list.get(i);
103
104             //UPPER is (I think) part of the SQL99 standard, and I'm not convinced it's universally available
105 // - should the syntax used here be defined by the Db specific adaptor perhaps, or at least
106 // possibly specified by the db adaptor (a DB specific OrderingTranslator hook)?
107 if (ord.isCaseInsensitive()) {
108                 ordComp.append("UPPER(");
109
110             }
111
112             Expression exp = ord.getSortSpec();
113
114             if (exp.getType() == Expression.OBJ_PATH) {
115                 appendObjPath(ordComp, exp);
116             } else if (exp.getType() == Expression.DB_PATH) {
117                 appendDbPath(ordComp, exp);
118             } else {
119                 throw new CayenneRuntimeException(
120                     "Unsupported ordering expression: " + exp);
121             }
122
123             //Close UPPER() modifier
124 if (ord.isCaseInsensitive()) {
125                 ordComp.append(")");
126             }
127
128             orderByColumnList.add(ordComp.toString());
129             
130             buf.append(ordComp.toString());
131
132             // "ASC" is a noop, omit it from the query
133 if (!ord.isAscending()) {
134                 buf.append(" DESC");
135             }
136         }
137
138         return buf.length() > 0 ? buf.toString() : null;
139     }
140
141     /**
142      * Returns the column expressions (not Expressions) used in
143      * the order by clause. E.g., in the case of an case-insensitive
144      * order by, an element of the list would be
145      * <code>UPPER(&lt;column reference&gt;)</code>
146      */
147     public List JavaDoc getOrderByColumnList() {
148         return orderByColumnList;
149     }
150 }
151
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