SLAPD-SQL(5) File Formats Manual SLAPD-SQL(5)
slapd-sql - SQL backend to slapd
ETCDIR/slapd.conf
The primary purpose of this slapd(8) backend is to PRESENT
information stored in some RDBMS as an LDAP subtree without any
programming (some SQL and maybe stored procedures can't be considered
programming, anyway ;).
That is, for example, when you (some ISP) have account information
you use in an RDBMS, and want to use modern solutions that expect
such information in LDAP (to authenticate users, make email lookups
etc.). Or you want to synchronize or distribute information between
different sites/applications that use RDBMSes and/or LDAP. Or
whatever else...
It is NOT designed as a general-purpose backend that uses RDBMS
instead of BerkeleyDB (as the standard BDB backend does), though it
can be used as such with several limitations. You can take a look at
http://www.openldap.org/faq/index.cgi?file=378 (OpenLDAP
FAQ-O-Matic/General LDAP FAQ/Directories vs. conventional databases)
to find out more on this point.
The idea (detailed below) is to use some meta-information to
translate LDAP queries to SQL queries, leaving relational schema
untouched, so that old applications can continue using it without any
modifications. This allows SQL and LDAP applications to inter-
operate without replication, and exchange data as needed.
The SQL backend is designed to be tunable to virtually any relational
schema without having to change source (through that meta-information
mentioned). Also, it uses ODBC to connect to RDBMSes, and is highly
configurable for SQL dialects RDBMSes may use, so it may be used for
integration and distribution of data on different RDBMSes, OSes,
hosts etc., in other words, in highly heterogeneous environment.
This backend is experimental.
These slapd.conf options apply to the SQL backend database, which
means that they must follow a "database sql" line and come before any
subsequent "backend" or "database" lines. Other database options not
specific to this backend are described in the slapd.conf(5) manual
page.
dbname <datasource name>
The name of the ODBC datasource to use.
dbhost <hostname>
dbpasswd <password>
dbuser <username>
The three above options are generally unneeded, because this
information is taken from the datasource specified by the
dbname directive. They allow to override datasource settings.
Also, several RDBMS' drivers tend to require explicit passing
of user/password, even if those are given in datasource (Note:
dbhost is currently ignored).
These options specify SQL query templates for scoping searches.
subtree_cond <SQL expression>
Specifies a where-clause template used to form a subtree
search condition (dn="(.+,)?<dn>$"). It may differ from one
SQL dialect to another (see samples). By default, it is
constructed based on the knowledge about how to normalize DN
values (e.g. "<upper_func>(ldap_entries.dn) LIKE
CONCAT('%',?)"); see upper_func, upper_needs_cast,
concat_pattern and strcast_func in "HELPER CONFIGURATION" for
details.
children_cond <SQL expression>
Specifies a where-clause template used to form a children
search condition (dn=".+,<dn>$"). It may differ from one SQL
dialect to another (see samples). By default, it is
constructed based on the knowledge about how to normalize DN
values (e.g. "<upper_func>(ldap_entries.dn) LIKE
CONCAT('%,',?)"); see upper_func, upper_needs_cast,
concat_pattern and strcast_func in "HELPER CONFIGURATION" for
details.
use_subtree_shortcut { YES | no }
Do not use the subtree condition when the searchBase is the
database suffix, and the scope is subtree; rather collect all
entries.
These options specify SQL query templates for loading schema mapping
meta-information, adding and deleting entries to ldap_entries, etc.
All these and subtree_cond should have the given default values. For
the current value it is recommended to look at the sources, or in the
log output when slapd starts with "-d 5" or greater. Note that the
parameter number and order must not be changed.
oc_query <SQL expression>
The query that is used to collect the objectClass mapping data
from table ldap_oc_mappings; see "METAINFORMATION USED" for
details. The default is "SELECT id, name, keytbl, keycol,
create_proc, delete_proc, expect_return FROM
ldap_oc_mappings".
at_query <SQL expression>
The query that is used to collect the attributeType mapping
data from table ldap_attr_mappings; see "METAINFORMATION USED"
for details. The default is "SELECT name, sel_expr,
from_tbls, join_where, add_proc, delete_proc, param_order,
expect_return FROM ldap_attr_mappings WHERE oc_map_id=?".
id_query <SQL expression>
The query that is used to map a DN to an entry in table
ldap_entries; see "METAINFORMATION USED" for details. The
default is "SELECT id,keyval,oc_map_id,dn FROM ldap_entries
WHERE <DN match expr>", where <DN match expr> is constructed
based on the knowledge about how to normalize DN values (e.g.
"dn=?" if no means to uppercase strings are available;
typically, "<upper_func>(dn)=?" is used); see upper_func,
upper_needs_cast, concat_pattern and strcast_func in "HELPER
CONFIGURATION" for details.
insentry_stmt <SQL expression>
The statement that is used to insert a new entry in table
ldap_entries; see "METAINFORMATION USED" for details. The
default is "INSERT INTO ldap_entries (dn, oc_map_id, parent,
keyval) VALUES (?, ?, ?, ?)".
delentry_stmt <SQL expression>
The statement that is used to delete an existing entry from
table ldap_entries; see "METAINFORMATION USED" for details.
The default is "DELETE FROM ldap_entries WHERE id=?".
delobjclasses_stmt <SQL expression>
The statement that is used to delete an existing entry's ID
from table ldap_objclasses; see "METAINFORMATION USED" for
details. The default is "DELETE FROM ldap_entry_objclasses
WHERE entry_id=?".
These statements are used to modify the default behavior of the
backend according to issues of the dialect of the RDBMS. The first
options essentially refer to string and DN normalization when
building filters. LDAP normalization is more than upper- (or
lower-)casing everything; however, as a reasonable trade-off, for
case-sensitive RDBMSes the backend can be instructed to uppercase
strings and DNs by providing the upper_func directive. Some RDBMSes,
to use functions on arbitrary data types, e.g. string constants,
requires a cast, which is triggered by the upper_needs_cast
directive. If required, a string cast function can be provided as
well, by using the strcast_func directive. Finally, a custom string
concatenation pattern may be required; it is provided by the
concat_pattern directive.
upper_func <SQL function name>
Specifies the name of a function that converts a given value
to uppercase. This is used for case insensitive matching when
the RDBMS is case sensitive. It may differ from one SQL
dialect to another (e.g. UCASE, UPPER or whatever; see
samples). By default, none is used, i.e. strings are not
uppercased, so matches may be case sensitive.
upper_needs_cast { NO | yes }
Set this directive to yes if upper_func needs an explicit cast
when applied to literal strings. A cast in the form CAST
(<arg> AS VARCHAR(<max DN length>)) is used, where <max DN
length> is builtin in back-sql; see macro BACKSQL_MAX_DN_LEN
(currently 255; note that slapd's builtin limit, in macro
SLAP_LDAPDN_MAXLEN, is set to 8192). This is experimental and
may change in future releases.
strcast_func <SQL function name>
Specifies the name of a function that converts a given value
to a string for appropriate ordering. This is used in "SELECT
DISTINCT" statements for strongly typed RDBMSes with little
implicit casting (like PostgreSQL), when a literal string is
specified. This is experimental and may change in future
releases.
concat_pattern <pattern>
This statement defines the pattern that is used to concatenate
strings. The pattern MUST contain two question marks, '?',
that will be replaced by the two strings that must be
concatenated. The default value is CONCAT(?,?); a form that
is known to be highly portable (IBM db2, PostgreSQL) is ?||?,
but an explicit cast may be required when operating on literal
strings: CAST(?||? AS VARCHAR(<length>)). On some RDBMSes
(IBM db2, MSSQL) the form ?+? is known to work as well.
Carefully check the documentation of your RDBMS or stay with
the examples for supported ones. This is experimental and may
change in future releases.
aliasing_keyword <string>
Define the aliasing keyword. Some RDBMSes use the word "AS"
(the default), others don't use any.
aliasing_quote <string>
Define the quoting char of the aliasing keyword. Some RDBMSes
don't require any (the default), others may require single or
double quotes.
has_ldapinfo_dn_ru { NO | yes }
Explicitly inform the backend whether the dn_ru column (DN in
reverse uppercased form) is present in table ldap_entries.
Overrides automatic check (this is required, for instance, by
PostgreSQL/unixODBC). This is experimental and may change in
future releases.
fail_if_no_mapping { NO | yes }
When set to yes it forces attribute write operations to fail
if no appropriate mapping between LDAP attributes and SQL data
is available. The default behavior is to ignore those changes
that cannot be mapped. It has no impact on objectClass
mapping, i.e. if the structuralObjectClass of an entry cannot
be mapped to SQL by looking up its name in ldap_oc_mappings,
an add operation will fail regardless of the
fail_if_no_mapping switch; see section "METAINFORMATION USED"
for details. This is experimental and may change in future
releases.
allow_orphans { NO | yes }
When set to yes orphaned entries (i.e. without the parent
entry in the database) can be added. This option should be
used with care, possibly in conjunction with some special rule
on the RDBMS side that dynamically creates the missing parent.
baseObject [ <filename> ]
Instructs the database to create and manage an in-memory
baseObject entry instead of looking for one in the RDBMS. If
the (optional) <filename> argument is given, the entry is read
from that file in LDIF(5) format; otherwise, an entry with
objectClass extensibleObject is created based on the contents
of the RDN of the baseObject. This is particularly useful
when ldap_entries information is stored in a view rather than
in a table, and union is not supported for views, so that the
view can only specify one rule to compute the entry structure
for one objectClass. This topic is discussed further in
section "METAINFORMATION USED". This is experimental and may
change in future releases.
create_needs_select { NO | yes }
Instructs the database whether or not entry creation in table
ldap_entries needs a subsequent select to collect the
automatically assigned ID, instead of being returned by a
stored procedure.
fetch_attrs <attrlist>
fetch_all_attrs { NO | yes }
The first statement allows one to provide a list of attributes
that must always be fetched in addition to those requested by
any specific operation, because they are required for the
proper usage of the backend. For instance, all attributes
used in ACLs should be listed here. The second statement is a
shortcut to require all attributes to be always loaded. Note
that the dynamically generated attributes, e.g.
hasSubordinates, entryDN and other implementation dependent
attributes are NOT generated at this point, for consistency
with the rest of slapd. This may change in the future.
check_schema { YES | no }
Instructs the database to check schema adherence of entries
after modifications, and structural objectClass chain when
entries are built. By default it is set to yes.
sqllayer <name> [...]
Loads the layer <name> onto a stack of helpers that are used
to map DNs from LDAP to SQL representation and vice-versa.
Subsequent args are passed to the layer configuration routine.
This is highly experimental and should be used with extreme
care. The API of the layers is not frozen yet, so it is
unpublished.
autocommit { NO | yes }
Activates autocommit; by default, it is off.
Almost everything mentioned later is illustrated in examples located
in the servers/slapd/back-sql/rdbms_depend/ directory in the OpenLDAP
source tree, and contains scripts for generating sample database for
Oracle, MS SQL Server, mySQL and more (including PostgreSQL and IBM
db2).
The first thing that one must arrange is what set of LDAP object
classes can present your RDBMS information.
The easiest way is to create an objectClass for each entity you had
in ER-diagram when designing your relational schema. Any relational
schema, no matter how normalized it is, was designed after some model
of your application's domain (for instance, accounts, services etc.
in ISP), and is used in terms of its entities, not just tables of
normalized schema. It means that for every attribute of every such
instance there is an effective SQL query that loads its values.
Also you might want your object classes to conform to some of the
standard schemas like inetOrgPerson etc.
Nevertheless, when you think it out, we must define a way to
translate LDAP operation requests to (a series of) SQL queries. Let
us deal with the SEARCH operation.
Example: Let's suppose that we store information about persons
working in our organization in two tables:
PERSONS PHONES
---------- -------------
id integer id integer
first_name varchar pers_id integer references persons(id)
last_name varchar phone
middle_name varchar
...
(PHONES contains telephone numbers associated with persons). A
person can have several numbers, then PHONES contains several records
with corresponding pers_id, or no numbers (and no records in PHONES
with such pers_id). An LDAP objectclass to present such information
could look like this:
person
-------
MUST cn
MAY telephoneNumber $ firstName $ lastName
...
To fetch all values for cn attribute given person ID, we construct
the query:
SELECT CONCAT(persons.first_name,' ',persons.last_name)
AS cn FROM persons WHERE persons.id=?
for telephoneNumber we can use:
SELECT phones.phone AS telephoneNumber FROM persons,phones
WHERE persons.id=phones.pers_id AND persons.id=?
If we wanted to service LDAP requests with filters like
(telephoneNumber=123*), we would construct something like:
SELECT ... FROM persons,phones
WHERE persons.id=phones.pers_id
AND persons.id=?
AND phones.phone like '%1%2%3%'
(note how the telephoneNumber match is expanded in multiple wildcards
to account for interspersed ininfluential chars like spaces, dashes
and so; this occurs by design because telephoneNumber is defined
after a specially recognized syntax). So, if we had information
about what tables contain values for each attribute, how to join
these tables and arrange these values, we could try to automatically
generate such statements, and translate search filters to SQL WHERE
clauses.
To store such information, we add three more tables to our schema and
fill it with data (see samples):
ldap_oc_mappings (some columns are not listed for clarity)
---------------
id=1
name="person"
keytbl="persons"
keycol="id"
This table defines a mapping between objectclass (its name held in
the "name" column), and a table that holds the primary key for
corresponding entities. For instance, in our example, the person
entity, which we are trying to present as "person" objectclass,
resides in two tables (persons and phones), and is identified by the
persons.id column (that we will call the primary key for this
entity). Keytbl and keycol thus contain "persons" (name of the
table), and "id" (name of the column).
ldap_attr_mappings (some columns are not listed for clarity)
-----------
id=1
oc_map_id=1
name="cn"
sel_expr="CONCAT(persons.first_name,' ',persons.last_name)"
from_tbls="persons"
join_where=NULL
************
id=<n>
oc_map_id=1
name="telephoneNumber"
sel_expr="phones.phone"
from_tbls="persons,phones"
join_where="phones.pers_id=persons.id"
This table defines mappings between LDAP attributes and SQL queries
that load their values. Note that, unlike LDAP schema, these are not
attribute types - the attribute "cn" for "person" objectclass can
have its values in different tables than "cn" for some other
objectclass, so attribute mappings depend on objectclass mappings
(unlike attribute types in LDAP schema, which are indifferent to
objectclasses). Thus, we have oc_map_id column with link to
oc_mappings table.
Now we cut the SQL query that loads values for a given attribute into
3 parts. First goes into sel_expr column - this is the expression we
had between SELECT and FROM keywords, which defines WHAT to load.
Next is table list - text between FROM and WHERE keywords. It may
contain aliases for convenience (see examples). The last is part of
the where clause, which (if it exists at all) expresses the condition
for joining the table containing values with the table containing the
primary key (foreign key equality and such). If values are in the
same table as the primary key, then this column is left NULL (as for
cn attribute above).
Having this information in parts, we are able to not only construct
queries that load attribute values by id of entry (for this we could
store SQL query as a whole), but to construct queries that load id's
of objects that correspond to a given search filter (or at least part
of it). See below for examples.
ldap_entries
------------
id=1
dn=<dn you choose>
oc_map_id=...
parent=<parent record id>
keyval=<value of primary key>
This table defines mappings between DNs of entries in your LDAP tree,
and values of primary keys for corresponding relational data. It has
recursive structure (parent column references id column of the same
table), which allows you to add any tree structure(s) to your flat
relational data. Having id of objectclass mapping, we can determine
table and column for primary key, and keyval stores value of it, thus
defining the exact tuple corresponding to the LDAP entry with this
DN.
Note that such design (see exact SQL table creation query) implies
one important constraint - the key must be an integer. But all that
I know about well-designed schemas makes me think that it's not very
narrow ;) If anyone needs support for different types for keys - he
may want to write a patch, and submit it to OpenLDAP ITS, then I'll
include it.
Also, several users complained that they don't really need very
structured trees, and they don't want to update one more table every
time they add or delete an instance in the relational schema. Those
people can use a view instead of a real table for ldap_entries,
something like this (by Robin Elfrink):
CREATE VIEW ldap_entries (id, dn, oc_map_id, parent, keyval)
AS
SELECT 0, UPPER('o=MyCompany,c=NL'),
3, 0, 'baseObject' FROM unixusers WHERE userid='root'
UNION
SELECT (1000000000+userid),
UPPER(CONCAT(CONCAT('cn=',gecos),',o=MyCompany,c=NL')),
1, 0, userid FROM unixusers
UNION
SELECT (2000000000+groupnummer),
UPPER(CONCAT(CONCAT('cn=',groupnaam),',o=MyCompany,c=NL')),
2, 0, groupnummer FROM groups;
If your RDBMS does not support unions in views, only one objectClass
can be mapped in ldap_entries, and the baseObject cannot be created;
in this case, see the baseObject directive for a possible workaround.
Having meta-information loaded, the SQL backend uses these tables to
determine a set of primary keys of candidates (depending on search
scope and filter). It tries to do it for each objectclass registered
in ldap_objclasses.
Example: for our query with filter (telephoneNumber=123*) we would
get the following query generated (which loads candidate IDs)
SELECT ldap_entries.id,persons.id, 'person' AS objectClass,
ldap_entries.dn AS dn
FROM ldap_entries,persons,phones
WHERE persons.id=ldap_entries.keyval
AND ldap_entries.objclass=?
AND ldap_entries.parent=?
AND phones.pers_id=persons.id
AND (phones.phone LIKE '%1%2%3%')
(for ONELEVEL search) or "... AND dn=?" (for BASE search) or "... AND
dn LIKE '%?'" (for SUBTREE)
Then, for each candidate, we load the requested attributes using per-
attribute queries like
SELECT phones.phone AS telephoneNumber
FROM persons,phones
WHERE persons.id=? AND phones.pers_id=persons.id
Then, we use test_filter() from the frontend API to test the entry
for a full LDAP search filter match (since we cannot effectively make
sense of SYNTAX of corresponding LDAP schema attribute, we translate
the filter into the most relaxed SQL condition to filter candidates),
and send it to the user.
ADD, DELETE, MODIFY and MODRDN operations are also performed on per-
attribute meta-information (add_proc etc.). In those fields one can
specify an SQL statement or stored procedure call which can add, or
delete given values of a given attribute, using the given entry
keyval (see examples -- mostly PostgreSQL, ORACLE and MSSQL - since
as of this writing there are no stored procs in MySQL).
We just add more columns to ldap_oc_mappings and ldap_attr_mappings,
holding statements to execute (like create_proc, add_proc, del_proc
etc.), and flags governing the order of parameters passed to those
statements. Please see samples to find out what are the parameters
passed, and other information on this matter - they are self-
explanatory for those familiar with the concepts expressed above.
First of all, let's recall that among other major differences to the
complete LDAP data model, the above illustrated concept does not
directly support such features as multiple objectclasses per entry,
and referrals. Fortunately, they are easy to adopt in this scheme.
The SQL backend requires that one more table is added to the schema:
ldap_entry_objectclasses(entry_id,oc_name).
That table contains any number of objectclass names that
corresponding entries will possess, in addition to that mentioned in
mapping. The SQL backend automatically adds attribute mapping for
the "objectclass" attribute to each objectclass mapping that loads
values from this table. So, you may, for instance, have a mapping
for inetOrgPerson, and use it for queries for "person" objectclass...
Referrals used to be implemented in a loose manner by adding an extra
table that allowed any entry to host a "ref" attribute, along with a
"referral" extra objectClass in table ldap_entry_objclasses. In the
current implementation, referrals are treated like any other user-
defined schema, since "referral" is a structural objectclass. The
suggested practice is to define a "referral" entry in
ldap_oc_mappings, holding a naming attribute, e.g. "ou" or "cn", a
"ref" attribute, containing the url; in case multiple referrals per
entry are needed, a separate table for urls can be created, where
urls are mapped to the respective entries. The use of the naming
attribute usually requires to add an "extensibleObject" value to
ldap_entry_objclasses.
As previously stated, this backend should not be considered a
replacement of other data storage backends, but rather a gateway to
existing RDBMS storages that need to be published in LDAP form.
The hasSubordintes operational attribute is honored by back-sql in
search results and in compare operations; it is partially honored
also in filtering. Owing to design limitations, a (brain-dead?)
filter of the form (!(hasSubordinates=TRUE)) will give no results
instead of returning all the leaf entries, because it actually
expands into ... AND NOT (1=1). If you need to find all the leaf
entries, please use (hasSubordinates=FALSE) instead.
A directoryString value of the form "__First___Last_" (where
underscores mean spaces, ASCII 0x20 char) corresponds to its
prettified counterpart "First_Last"; this is not currently honored by
back-sql if non-prettified data is written via RDBMS; when non-
prettified data is written through back-sql, the prettified values
are actually used instead.
When the ldap_entry_objclasses table is empty, filters on the
objectClass attribute erroneously result in no candidates. A
workaround consists in adding at least one row to that table, no
matter if valid or not.
The proxy cache overlay allows caching of LDAP search requests
(queries) in a local database. See slapo-pcache(5) for details.
There are example SQL modules in the slapd/back-sql/rdbms_depend/
directory in the OpenLDAP source tree.
The sql backend honors access control semantics as indicated in
slapd.access(5) (including the disclose access privilege when enabled
at compile time).
ETCDIR/slapd.conf
default slapd configuration file
slapd.conf(5), slapd(8).
This page is part of the OpenLDAP (an open source implementation of
the Lightweight Directory Access Protocol) project. Information
about the project can be found at ⟨http://www.openldap.org/⟩. If you
have a bug report for this manual page, see
⟨http://www.openldap.org/its/⟩. This page was obtained from the
project's upstream Git repository
⟨git://git.openldap.org/openldap.git⟩ on 2017-07-05. If you discover
any rendering problems in this HTML version of the page, or you
believe there is a better or more up-to-date source for the page, or
you have corrections or improvements to the information in this
COLOPHON (which is not part of the original manual page), send a mail
to man-pages@man7.org
OpenLDAP LDVERSION RELEASEDATE SLAPD-SQL(5)
Pages that refer to this page: slapd.backends(5), slapo-pcache(5)