Provided by: slapd_2.5.18+dfsg-0ubuntu0.22.04.2_amd64 
NAME
slapd-sql - SQL backend to slapd
SYNOPSIS
/etc/ldap/slapd.conf
DESCRIPTION
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 LMDB (as the
standard MDB 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.
CONFIGURATION
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.
DATA SOURCE CONFIGURATION
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).
SCOPING CONFIGURATION
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.
STATEMENT CONFIGURATION
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=?".
HELPER CONFIGURATION
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.
METAINFORMATION USED
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=',groupname),',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.
TYPICAL SQL BACKEND OPERATION
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.
COMMON TECHNIQUES
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.
CAVEATS
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 hasSubordinates 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.
BUGS
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.
PROXY CACHE OVERLAY
The proxy cache overlay allows caching of LDAP search requests (queries) in a local
database. See slapo-pcache(5) for details.
EXAMPLES
There are example SQL modules in the slapd/back-sql/rdbms_depend/ directory in the
OpenLDAP source tree.
ACCESS CONTROL
The sql backend honors access control semantics as indicated in slapd.access(5) (including
the disclose access privilege when enabled at compile time).
FILES
/etc/ldap/slapd.conf
default slapd configuration file
SEE ALSO
slapd.conf(5), slapd(8).