KDb

KDbRelationship.h
1/* This file is part of the KDE project
2 Copyright (C) 2003-2017 Jarosław Staniek <staniek@kde.org>
3
4 This library is free software; you can redistribute it and/or
5 modify it under the terms of the GNU Library General Public
6 License as published by the Free Software Foundation; either
7 version 2 of the License, or (at your option) any later version.
8
9 This library is distributed in the hope that it will be useful,
10 but WITHOUT ANY WARRANTY; without even the implied warranty of
11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12 Library General Public License for more details.
13
14 You should have received a copy of the GNU Library General Public License
15 along with this library; see the file COPYING.LIB. If not, write to
16 the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
17 * Boston, MA 02110-1301, USA.
18 */
19
20#ifndef KDB_RELATIONSHIP_H
21#define KDB_RELATIONSHIP_H
22
23#include "KDbField.h"
24
25/*! KDbRelationship provides information about one-to-many relationship between two tables.
26 Relationship is defined by a pair of (potentially multi-field) indices:
27 - "one" or "master" side: unique key
28 - "many" or "details" side: referenced foreign key
29 <pre>
30 [unique key, master] ----< [foreign key, details]
31 </pre>
32
33 In this documentation, we will call table that owns fields of "one" side as
34 "master side of the relationship", and the table that owns foreign key fields of
35 as "details side of the relationship".
36 Use masterTable(), and detailsTable() to get one-side table and many-side table, respectively.
37
38 Note: some engines (e.g. MySQL with InnoDB) requires that indices at both sides
39 have to be explicitly created.
40
41 @todo (js) It is planned that this will be handled by KDb internally and transparently.
42
43 Each (of the two) key can be defined (just like index) as list of fields owned by one table.
44 Indeed, relationship info can retrieved from KDbRelationship object in two ways:
45 -# pair of indices; use masterIndex(), detailsIndex() for that
46 -# ordered list of field pairs (<master-side-field, details-side-field>); use fieldPairs() for that
47
48 No assigned objects (like fields, indices) are owned by KDbRelationship object. The exception is that
49 list of field-pairs is internally created (on demand) and owned.
50
51 KDbRelationship object is owned by KDbIndexSchema object (the one that is defined at master-side of the
52 relationship).
53 Note also that KDbIndexSchema objects are owned by appropriate tables, so thus
54 there is implicit ownership between KDbTableSchema and KDbRelationship.
55
56 If KDbRelationship object is not attached to KDbIndexSchema object,
57 you should care about destroying it by hand.
58
59 Example:
60 <pre>
61 ----------
62 ---r1--<| |
63 | Table A [uk]----r3---<
64 ---r2--<| |
65 ----------
66 </pre>
67 Table A has two relationships (r1, r2) at details side and one (r3) at master side.
68 [uk] stands for unique key.
69*/
70
71class KDbIndexSchema;
72class KDbTableSchema;
73class KDbQuerySchema;
74
75class KDB_EXPORT KDbRelationship
76{
77public:
78 typedef QList<KDbRelationship*> List;
79 typedef QList<KDbRelationship*>::ConstIterator ListIterator;
80
81 /**
82 * @brief Creates a new uninitialized KDbRelationship object
83 */
84 KDbRelationship();
85
86 /**
87 * @brief Creates a new KDbRelationship object and initialises it using setIndices()
88 *
89 * If setIndices() failed, object is still uninitialised. Check this using isEmpty().
90 */
91 KDbRelationship(KDbIndexSchema* masterIndex, KDbIndexSchema* detailsIndex);
92
93 virtual ~KDbRelationship();
94
95 //! Assigns @a other to this object returns a reference to this object.
96 //! @since 3.1
97 KDbRelationship& operator=(KDbRelationship &other);
98
99 //! @return true if this relationship is the same as @a other
100 //! Relationships are equal if they have the same details and master indices are equal
101 //! @since 3.1
102 bool operator==(const KDbRelationship& other) const;
103
104 //! @return @c true if this object is not equal to @a other; otherwise returns @c false.
105 //! @since 3.1
106 inline bool operator!=(const KDbRelationship &other) const { return !operator==(other); }
107
108 /*! @return index defining master side of this relationship
109 or @c nullptr if there is no information defined. */
110 KDbIndexSchema* masterIndex();
111
112 //! @overload
113 const KDbIndexSchema* masterIndex() const;
114
115 /*! @return index defining referenced side of this relationship.
116 or @c nullptr if there is no information defined. */
117 KDbIndexSchema* detailsIndex();
118
119 //! @overload
120 const KDbIndexSchema* detailsIndex() const;
121
122 /**
123 * Returns ordered list of field pairs, alternative representation of relationship
124 *
125 * @c nullptr is returned if there is no information defined.
126 * Each pair has a form of <master-side-field, details-side-field>.
127 */
128 KDbField::PairList* fieldPairs();
129
130 //! @overload
131 const KDbField::PairList* fieldPairs() const;
132
133 //! @return true if there are no master-details pairs in this relationship object
134 //! @see fieldPairs()
135 bool isEmpty() const;
136
137 /*! @return table assigned at "master / one" side of this relationship.
138 or @c nullptr if there is no information defined. */
139 KDbTableSchema* masterTable();
140
141 //! @overload
142 const KDbTableSchema* masterTable() const;
143
144 /*! @return table assigned at "details / many / foreign" side of this relationship.
145 or @c nullptr if there is no information defined. */
146 KDbTableSchema* detailsTable();
147
148 //! @overload
149 const KDbTableSchema* detailsTable() const;
150
151 /*! Sets @a masterIndex and @a detailsIndex indices for this relationship.
152 This also sets information about tables for master- and details- sides.
153 Notes:
154 - both indices must contain the same number of fields
155 - both indices must not be owned by the same table, and table (owner) must be not null.
156 - corresponding field types must be the same
157 - corresponding field types' signedness must be the same
158 If above rules are not fulfilled, information about this relationship is cleared.
159 On success, this KDbRelationship object is detached from previous KDbIndexSchema objects that were
160 assigned before, and new are attached.
161 */
162 bool setIndices(KDbIndexSchema* masterIndex, KDbIndexSchema* detailsIndex);
163
164protected:
165 KDbRelationship(KDbQuerySchema *query, KDbField *field1, KDbField *field2);
166
167 friend class KDbConnection;
168 friend class KDbTableSchema;
169 friend class KDbQuerySchema;
170 friend class KDbIndexSchema;
171
172private:
173 class Private;
174 Private * const d;
175};
176
177#endif
Provides database connection, allowing queries and data modification.
Meta-data for a field.
Definition KDbField.h:72
Provides information about database index that can be created for a database table.
KDbQuerySchema provides information about database query.
bool operator==(const QGraphicsApiFilter &reference, const QGraphicsApiFilter &sample)
bool operator!=(const QGraphicsApiFilter &reference, const QGraphicsApiFilter &sample)
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