1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one
3 * or more contributor license agreements. See the NOTICE file
4 * distributed with this work for additional information
5 * regarding copyright ownership. The ASF licenses this file
6 * to you under the Apache License, Version 2.0 (the
7 * "License"); you may not use this file except in compliance
8 * with the License. You may obtain a copy of the License at
9 *
10 * http://www.apache.org/licenses/LICENSE-2.0
11 *
12 * Unless required by applicable law or agreed to in writing,
13 * software distributed under the License is distributed on an
14 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
15 * KIND, either express or implied. See the License for the
16 * specific language governing permissions and limitations
17 * under the License.
18 *
19 */
20 package org.apache.directory.server.xdbm.search;
21
22
23 import org.apache.directory.api.ldap.model.entry.Entry;
24 import org.apache.directory.api.ldap.model.exception.LdapException;
25 import org.apache.directory.api.ldap.model.filter.ExprNode;
26 import org.apache.directory.server.core.api.partition.PartitionTxn;
27 import org.apache.directory.server.xdbm.IndexEntry;
28
29
30 /**
31 * Evaluates candidate entries to see if they match a filter expression.
32 *
33 * Evaluators contain various overloads to the evaluate method. Often a
34 * developer working in this region of the code may wonder when to use one
35 * override verses another. The overload taking an IndexEntry argument is
36 * specifically suited for use when there is the possibility of multiple entry
37 * lookups from the master table. If the same candidate in the form of an
38 * IndexEntry is evaluated more then this overload is more efficient since it
39 * stores the looked up entry in the IndexEntry preventing multiple lookups.
40 *
41 * If the index entry is already populated with an entry object, and some
42 * evaluation is required then it is preferrable to use the overload that
43 * takes a Long id instead. Likewise if it is known in advance that the
44 * expression is a leaf node built on an indexed attribute then the overload
45 * with the Long id argument is also preferrable unless an IndexEntry already
46 * exists in which case it makes no difference.
47 *
48 * The overload taking the ServerEntry itself is a last resort option and ok
49 * to use when it is known that no index exists for the attributes of
50 * Evaluators based on leaf expressions.
51 *
52 * @author <a href="mailto:dev@directory.apache.org">Apache Directory Project</a>
53 */
54 public interface Evaluator<N extends ExprNode>
55 {
56 /**
57 * Evaluates a candidate to determine if a filter expression selects it.
58 * If an IndexEntry does has a null reference to the entry object, this
59 * Evaluator may set it if it has to access the full entry within the
60 * master table of the store. Subsequent evaluations on the IndexEntry
61 * then need not access the store to retreive the entry if they need to
62 * access it's attributes.
63 *
64 * @param partitionTxn The transaction to use
65 * @param entry the index record of the entry to evaluate
66 * @return true if filter selects the candidate false otherwise
67 * @throws LdapException if there are faults during evaluation
68 */
69 boolean evaluate( PartitionTxn partitionTxn, IndexEntry<?, String> entry ) throws LdapException;
70
71
72 /**
73 * Evaluates whether or not a candidate, satisfies the expression
74 * associated with this Evaluator .
75 *
76 * @param entry the candidate entry
77 * @return true if filter selects the candidate false otherwise
78 * @throws LdapException if there are faults during evaluation
79 */
80 boolean evaluate( Entry entry ) throws LdapException;
81
82
83 /**
84 * Gets the expression used by this expression Evaluator.
85 *
86 * @return the AST for the expression
87 */
88 N getExpression();
89
90
91 /**
92 * Pretty-print an Evaluator
93 * @param tabs The tabs to add before the evaluator
94 * @return The pretty-printed evaluator and its descendants
95 */
96 String toString( String tabs );
97 }