1 .TH SLAPD-SQL 5 "RELEASEDATE" "OpenLDAP LDVERSION"
4 slapd-sql \- SQL backend to slapd
8 The primary purpose of this
10 backend is to PRESENT information stored in some RDBMS as an LDAP subtree
11 without any programming (some SQL and maybe stored procedures can't be
12 considered programming, anyway ;).
14 That is, for example, when you (some ISP) have account information you
15 use in an RDBMS, and want to use modern solutions that expect such
16 information in LDAP (to authenticate users, make email lookups etc.).
17 Or you want to synchronize or distribute information between different
18 sites/applications that use RDBMSes and/or LDAP.
21 It is NOT designed as a general-purpose backend that uses RDBMS instead
22 of BerkeleyDB (as the standard BDB backend does), though it can be
23 used as such with several limitations.
24 You can take a look at
25 .B http://www.openldap.org/faq/index.cgi?file=378
26 (OpenLDAP FAQ-O-Matic/General LDAP FAQ/Directories vs. conventional
27 databases) to find out more on this point.
29 The idea (detailed below) is to use some metainformation to translate
30 LDAP queries to SQL queries, leaving relational schema untouched, so
31 that old applications can continue using it without any
33 This allows SQL and LDAP applications to inter-operate without
34 replication, and exchange data as needed.
36 The SQL backend is designed to be tunable to virtually any relational
37 schema without having to change source (through that metainformation
39 Also, it uses ODBC to connect to RDBMSes, and is highly configurable
40 for SQL dialects RDBMSes may use, so it may be used for integration
41 and distribution of data on different RDBMSes, OSes, hosts etc., in
42 other words, in highly heterogeneous environment.
46 options apply to the SQL backend database.
47 That is, they must follow a "database sql" line and come before any
48 subsequent "backend" or "database" lines.
49 Other database options are described in the
53 .B dbname <datasource name>
54 The name of the ODBC datasource to use.
60 .B dbpasswd <password>
62 These three options are generally unneeded, because this information is already
63 taken from the datasource.
64 Use them if you need to override datasource settings.
65 Also, several RDBMS' drivers tend to require explicit passing of user/password,
66 even if those are given in datasource (Note:
68 is currently ignored).
71 .B subtree_cond <SQL expression>
72 Specifies a where-clause template used to form a subtree search condition
74 It may differ from one SQL dialect to another (see samples).
76 .B children_cond <SQL expression>
77 Specifies a where-clause template used to form a children search condition
79 It may differ from one SQL dialect to another (see samples).
81 .B oc_query <SQL expression>
83 .B "SELECT id, name, keytbl, keycol, create_proc, delete_proc, expect_return FROM ldap_oc_mappings"
85 .B at_query <SQL expression>
87 .B "SELECT name, sel_expr, from_tbls, join_where, add_proc, delete_proc, param_order, expect_return FROM ldap_attr_mappings WHERE oc_map_id=?"
89 .B insentry_query <SQL expression>
91 .B "INSERT INTO ldap_entries (dn, oc_map_id, parent, keyval) VALUES (?, ?, ?, ?)"
93 .B delentry_query <SQL expression>
95 .B "DELETE FROM ldap_entries WHERE id=?"
97 These four options specify SQL query templates for loading schema mapping
99 adding and deleting entries to ldap_entries, etc.
100 All these and subtree_cond should have the given default values.
101 For the current value it is recommended to look at the sources,
102 or in the log output when slapd starts with "-d 5" or greater.
103 Note that the parameter number and order must not be changed.
105 .B upper_func <SQL function name>
106 Specifies the name of a function that converts a given value to uppercase.
107 This is used for CIS matching when the RDBMS is case sensitive.
109 .B upper_needs_cast { yes | no }
110 Set this directive to
114 needs an explicit cast when applied to literal strings. The form
115 .B cast (<arg> as varchar(<max DN length>))
121 and may change in future releases.
123 .B concat_pattern <pattern>
124 This statement defines the
126 to be used to concatenate strings. The
128 MUST contain two question marks, '?', that will be replaced
129 by the two strings that must be concatenated. The default value is
131 a form that is known to be highly portable is
133 but an explicit cast may be required when operating on literal strings:
134 .BR "cast(?||? as varchar(<length>))".
135 On some RDBMSes the form
138 Carefully check the documentation of your RDBMS or stay with the examples
142 and may change in future releases.
144 .B strcast_func <SQL function name>
145 Specifies the name of a function that converts a given value to a string
146 for appropriate ordering. This is used in "SELECT DISTINCT" statements
147 for strongly typed RDBMSes with little implicit casting (like PostgreSQL),
148 when a literal string is specified.
151 and may change in future releases.
153 .B has_ldapinfo_dn_ru { yes | no }
154 Explicitly inform the backend whether the SQL schema has dn_ru column
155 (dn in reverse uppercased form) or not.
156 Overrides automatic check (required by PostgreSQL/unixODBC).
159 and may change in future releases.
162 .B fail_if_no_mapping { yes | no }
165 it forces write operations to fail if no appropriate mapping between LDAP
166 attributes and SQL data is available. The default behavior is to ignore
167 those changes that cannot be mapped correctly.
170 and may change in future releases.
172 .SH METAINFORMATION USED
174 Almost everything mentioned later is illustrated in examples located
176 .B servers/slapd/back-sql/rdbms_depend/
177 directory in the OpenLDAP source tree, and contains scripts for
178 generating sample database for Oracle, MS SQL Server, mySQL and more
179 (including PostgreSQL and IBM db2).
181 The first thing that one must arrange is what set of LDAP
182 object classes can present your RDBMS information.
184 The easiest way is to create an objectclass for each entity you had in
185 ER-diagram when designing your relational schema.
186 Any relational schema, no matter how normalized it is, was designed
187 after some model of your application's domain (for instance, accounts,
188 services etc. in ISP), and is used in terms of its entities, not just
189 tables of normalized schema.
190 It means that for every attribute of every such instance there is an
191 effective SQL query that loads its values.
193 Also you might want your object classes to conform to some of the standard
194 schemas like inetOrgPerson etc.
196 Nevertheless, when you think it out, we must define a way to translate
197 LDAP operation requests to (a series of) SQL queries.
198 Let us deal with the SEARCH operation.
201 Let's suppose that we store information about persons working in our
202 organization in two tables:
206 ---------- -------------
207 id integer id integer
208 first_name varchar pers_id integer references persons(id)
209 last_name varchar phone
214 (PHONES contains telephone numbers associated with persons).
215 A person can have several numbers, then PHONES contains several
216 records with corresponding pers_id, or no numbers (and no records in
217 PHONES with such pers_id).
218 An LDAP objectclass to present such information could look like this:
224 MAY telephoneNumber $ firstName $ lastName
228 To fetch all values for cn attribute given person ID, we construct the
232 SELECT CONCAT(persons.first_name,' ',persons.last_name)
233 AS cn FROM persons WHERE persons.id=?
236 for telephoneNumber we can use:
239 SELECT phones.phone AS telephoneNumber FROM persons,phones
240 WHERE persons.id=phones.pers_id AND persons.id=?
243 If we wanted to service LDAP requests with filters like
244 (telephoneNumber=123*), we would construct something like:
247 SELECT ... FROM persons,phones
248 WHERE persons.id=phones.pers_id
250 AND phones.phone like '123%'
253 So, if we had information about what tables contain values for each
254 attribute, how to join these tables and arrange these values, we could
255 try to automatically generate such statements, and translate search
256 filters to SQL WHERE clauses.
258 To store such information, we add three more tables to our schema
259 and fill it with data (see samples):
262 ldap_oc_mappings (some columns are not listed for clarity)
270 This table defines a mapping between objectclass (its name held in the
271 "name" column), and a table that holds the primary key for corresponding
273 For instance, in our example, the person entity, which we are trying
274 to present as "person" objectclass, resides in two tables (persons and
275 phones), and is identified by the persons.id column (that we will call
276 the primary key for this entity).
277 Keytbl and keycol thus contain "persons" (name of the table), and "id"
278 (name of the column).
281 ldap_attr_mappings (some columns are not listed for clarity)
286 sel_expr="CONCAT(persons.first_name,' ',persons.last_name)"
292 name="telephoneNumber"
293 sel_expr="phones.phone"
294 from_tbls="persons,phones"
295 join_where="phones.pers_id=persons.id"
298 This table defines mappings between LDAP attributes and SQL queries
299 that load their values.
300 Note that, unlike LDAP schema, these are not
302 - the attribute "cn" for "person" objectclass can
303 have its values in different tables than "cn" for some other objectclass,
304 so attribute mappings depend on objectclass mappings (unlike attribute
305 types in LDAP schema, which are indifferent to objectclasses).
306 Thus, we have oc_map_id column with link to oc_mappings table.
308 Now we cut the SQL query that loads values for a given attribute into 3 parts.
309 First goes into sel_expr column - this is the expression we had
310 between SELECT and FROM keywords, which defines WHAT to load.
311 Next is table list - text between FROM and WHERE keywords.
312 It may contain aliases for convenience (see examples).
313 The last is part of the where clause, which (if it exists at all) expresses the
314 condition for joining the table containing values with the table
315 containing the primary key (foreign key equality and such).
316 If values are in the same table as the primary key, then this column is
317 left NULL (as for cn attribute above).
319 Having this information in parts, we are able to not only construct
320 queries that load attribute values by id of entry (for this we could
321 store SQL query as a whole), but to construct queries that load id's
322 of objects that correspond to a given search filter (or at least part of
324 See below for examples.
332 parent=<parent record id>
333 keyval=<value of primary key>
336 This table defines mappings between DNs of entries in your LDAP tree,
337 and values of primary keys for corresponding relational data.
338 It has recursive structure (parent column references id column of the
339 same table), which allows you to add any tree structure(s) to your
340 flat relational data.
341 Having id of objectclass mapping, we can determine table and column
342 for primary key, and keyval stores value of it, thus defining the exact
343 tuple corresponding to the LDAP entry with this DN.
345 Note that such design (see exact SQL table creation query) implies one
346 important constraint - the key must be an integer.
347 But all that I know about well-designed schemas makes me think that it's
348 not very narrow ;) If anyone needs support for different types for
349 keys - he may want to write a patch, and submit it to OpenLDAP ITS,
350 then I'll include it.
352 Also, several people complained that they don't really need very
353 structured trees, and they don't want to update one more table every
354 time they add or delete an instance in the relational schema.
355 Those people can use a view instead of a real table for ldap_entries, something
356 like this (by Robin Elfrink):
359 CREATE VIEW ldap_entries (id, dn, oc_map_id, parent, keyval)
360 AS SELECT (1000000000+userid),
361 UPPER(CONCAT(CONCAT('cn=',gecos),',o=MyCompany,c=NL')),
362 1, 0, userid FROM unixusers UNION
363 SELECT (2000000000+groupnummer),
364 UPPER(CONCAT(CONCAT('cn=',groupnaam),',o=MyCompany,c=NL')),
365 2, 0, groupnummer FROM groups;
368 .SH Typical SQL backend operation
369 Having metainformation loaded, the SQL backend uses these tables to
370 determine a set of primary keys of candidates (depending on search
372 It tries to do it for each objectclass registered in ldap_objclasses.
375 for our query with filter (telephoneNumber=123*) we would get the following
376 query generated (which loads candidate IDs)
379 SELECT ldap_entries.id,persons.id, 'person' AS objectClass,
380 ldap_entries.dn AS dn
381 FROM ldap_entries,persons,phones
382 WHERE persons.id=ldap_entries.keyval
383 AND ldap_entries.objclass=?
384 AND ldap_entries.parent=?
385 AND phones.pers_id=persons.id
386 AND (phones.phone LIKE '123%')
389 (for ONELEVEL search)
390 or "... AND dn=?" (for BASE search)
391 or "... AND dn LIKE '%?'" (for SUBTREE)
393 Then, for each candidate, we load the requested attributes using
394 per-attribute queries like
397 SELECT phones.phone AS telephoneNumber
399 WHERE persons.id=? AND phones.pers_id=persons.id
402 Then, we use test_filter() from the frontend API to test the entry for a full
403 LDAP search filter match (since we cannot effectively make sense of
404 SYNTAX of corresponding LDAP schema attribute, we translate the filter
405 into the most relaxed SQL condition to filter candidates), and send it to
408 ADD, DELETE, MODIFY operations are also performed on per-attribute
409 metainformation (add_proc etc.).
410 In those fields one can specify an SQL statement or stored procedure
411 call which can add, or delete given values of a given attribute, using
412 the given entry keyval (see examples -- mostly ORACLE and MSSQL - since
413 there're no stored procs in mySQL).
415 We just add more columns to oc_mappings and attr_mappings, holding
416 statements to execute (like create_proc, add_proc, del_proc etc.), and
417 flags governing the order of parameters passed to those statements.
418 Please see samples to find out what are the parameters passed, and other
419 information on this matter - they are self-explanatory for those familiar
420 with concept expressed above.
422 .SH common techniques (referrals, multiclassing etc.)
423 First of all, let's remember that among other major differences to the
424 complete LDAP data model, the concept above does not directly support
425 such things as multiple objectclasses per entry, and referrals.
426 Fortunately, they are easy to adopt in this scheme.
427 The SQL backend suggests two more tables being added to the schema -
428 ldap_entry_objectclasses(entry_id,oc_name), and
429 ldap_referrals(entry_id,url).
431 The first contains any number of objectclass names that corresponding
432 entries will be found by, in addition to that mentioned in
434 The SQL backend automatically adds attribute mapping for the "objectclass"
435 attribute to each objectclass mapping that loads values from this table.
436 So, you may, for instance, have a mapping for inetOrgPerson, and use it
437 for queries for "person" objectclass...
439 The second table contains any number of referrals associated with a given entry.
440 The SQL backend automatically adds attribute mapping for "ref" attribute
441 to each objectclass mapping that loads values from this table.
442 So, if you add objectclass "referral" to this entry, and make one or
443 more tuples in ldap_referrals for this entry (they will be seen as
444 values of "ref" attribute), you will have slapd return a referral, as
445 described in the Administrators Guide.
448 There are example SQL modules in the slapd/back-sql/rdbms_depend/
449 directory in the OpenLDAP source tree.
453 default slapd configuration file
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