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Java > Open Source Codes > org > objectstyle > cayenne > access > util > PrefetchHelper


1 /* ====================================================================
2  *
3  * The ObjectStyle Group Software License, version 1.1
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6  * Copyright (c) 2002-2005, Andrei (Andrus) Adamchik and individual authors
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56 package org.objectstyle.cayenne.access.util;
57
58 import java.util.ArrayList JavaDoc;
59 import java.util.HashMap JavaDoc;
60 import java.util.List JavaDoc;
61 import java.util.ListIterator JavaDoc;
62 import java.util.Map JavaDoc;
63
64 import org.objectstyle.cayenne.CayenneRuntimeException;
65 import org.objectstyle.cayenne.DataObject;
66 import org.objectstyle.cayenne.ObjectId;
67 import org.objectstyle.cayenne.PersistenceState;
68 import org.objectstyle.cayenne.access.DataContext;
69 import org.objectstyle.cayenne.access.ToManyList;
70 import org.objectstyle.cayenne.exp.parser.ASTDbPath;
71 import org.objectstyle.cayenne.exp.parser.ASTIn;
72 import org.objectstyle.cayenne.exp.parser.ASTList;
73 import org.objectstyle.cayenne.map.DbRelationship;
74 import org.objectstyle.cayenne.map.ObjEntity;
75 import org.objectstyle.cayenne.map.ObjRelationship;
76 import org.objectstyle.cayenne.query.SelectQuery;
77
78 /**
79  * A helper class to resolve relationships in batches for the lists of objects. Used for
80  * performance tuning.
81  *
82  * @author Arndt Brenschede
83  */
84 public class PrefetchHelper {
85
86     /**
87      * Resolves a to-one relationship for a list of objects.
88      */
89     public static void resolveToOneRelations(
90             DataContext context,
91             List JavaDoc objects,
92             String JavaDoc relName) {
93
94         int len = objects.size();
95         if (len == 0) {
96             return;
97         }
98
99         List JavaDoc oids = null;
100
101         for (int i = 0; i < len; i++) {
102             DataObject sourceObject = (DataObject) objects.get(i);
103             DataObject targetObject = (DataObject) sourceObject.readProperty(relName);
104
105             if (targetObject.getPersistenceState() == PersistenceState.HOLLOW) {
106                 ObjectId oid = targetObject.getObjectId();
107
108                 if (oids == null) {
109                     oids = new ArrayList JavaDoc(len);
110                 }
111
112                 oids.add(oid);
113             }
114         }
115
116         if (oids != null) {
117             // this maybe suboptimal, cause it uses an OR .. OR .. OR .. expression
118 // instead of IN (..) - to be compatble with compound keys -
119 // however, it seems to be quite fast as well
120 SelectQuery sel = QueryUtils.selectQueryForIds(oids);
121             context.performQuery(sel);
122         }
123     }
124
125     /**
126      * Resolves a toMany relation for a list of objects.
127      * <p>
128      * WARNING: this is a bit of a hack - it works for my toMany's, but it possibly
129      * doesn't work in all cases.
130      * </p>
131      * <p>
132      * *** It definitly does not work for compound keys ***
133      * </p>
134      */
135     public static void resolveToManyRelations(
136             DataContext context,
137             List JavaDoc objects,
138             String JavaDoc relName) {
139
140         int nobjects = objects.size();
141         if (nobjects == 0)
142             return;
143
144         String JavaDoc dbKey = null;
145         Map JavaDoc listMap = new HashMap JavaDoc(nobjects);
146
147         // put the object-ids in a map for later assignment of the
148 // query results
149
150         for (int i = 0; i < nobjects; i++) {
151             DataObject object = (DataObject) objects.get(i);
152             ObjectId oid = object.getObjectId();
153             if (dbKey == null) {
154                 Map JavaDoc id = oid.getIdSnapshot();
155                 if (id.size() != 1) {
156                     throw new CayenneRuntimeException(
157                             "resolveToManyRelations expects single keys for now...");
158                 }
159                 dbKey = (String JavaDoc) id.keySet().iterator().next();
160             }
161             listMap.put(oid.getValueForAttribute(dbKey), new ArrayList JavaDoc());
162         }
163
164         ObjEntity ent = context.getEntityResolver().lookupObjEntity(
165                 (DataObject) objects.get(0));
166         ObjRelationship rel = (ObjRelationship) ent.getRelationship(relName);
167         ObjEntity destEnt = (ObjEntity) rel.getTargetEntity();
168
169         List JavaDoc dbRels = rel.getDbRelationships();
170
171         // sanity check
172 if (dbRels == null || dbRels.size() == 0) {
173             throw new CayenneRuntimeException("ObjRelationship '"
174                     + rel.getName()
175                     + "' is unmapped.");
176         }
177
178         // build a reverse DB path
179 // ...while reverse ObjRelationship may be absent,
180 // reverse DB must always be there...
181 StringBuffer JavaDoc buf = new StringBuffer JavaDoc();
182         ListIterator JavaDoc it = dbRels.listIterator(dbRels.size());
183         while (it.hasPrevious()) {
184             if (buf.length() > 0) {
185                 buf.append(".");
186             }
187             DbRelationship dbRel = (DbRelationship) it.previous();
188             DbRelationship reverse = dbRel.getReverseRelationship();
189
190             // another sanity check
191 if (reverse == null) {
192                 throw new CayenneRuntimeException("DbRelatitionship '"
193                         + dbRel.getName()
194                         + "' has no reverse relationship");
195             }
196
197             buf.append(reverse.getName());
198         }
199
200         // do the query
201
202         ASTDbPath dbpath = new ASTDbPath(buf.toString());
203         ASTList listExp = new ASTList(objects);
204         SelectQuery sel = new SelectQuery(destEnt, new ASTIn(dbpath, listExp));
205         sel.setFetchingDataRows(true);
206         List JavaDoc results = context.performQuery(sel);
207
208         // sort the resulting objects into individual lists for each source object
209
210         List JavaDoc destObjects = context.objectsFromDataRows(destEnt, results, false, false);
211         int nrows = destObjects.size();
212         for (int k = 0; k < nrows; k++) {
213             Map JavaDoc row = (Map JavaDoc) results.get(k);
214             ((List JavaDoc) listMap.get(row.get(dbKey))).add(destObjects.get(k));
215         }
216
217         // and finally set these lists in the relation targets
218 for (int i = 0; i < nobjects; i++) {
219             DataObject object = (DataObject) objects.get(i);
220             ObjectId oid = object.getObjectId();
221             List JavaDoc list = (List JavaDoc) listMap.get(oid.getValueForAttribute(dbKey));
222
223             ((ToManyList) object.readPropertyDirectly(relName)).setObjectList(list);
224         }
225     }
226 }
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