Go to main content

man pages section 5: File Formats

Exit Print View

Updated: Wednesday, February 9, 2022

slapd-sql (5oldap)


slapd-sql - SQL backend to slapd




SLAPD-SQL(5oldap)                                            SLAPD-SQL(5oldap)

       slapd-sql - SQL backend to slapd


       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 replica-
       tion, 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 subse-
       quent "backend" or "database" lines.  Other database options  not  spe-
       cific 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

       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, cre-
              ate_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; typi-
              cally,   "<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 ta-
              ble 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

       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 DIS-
              TINCT"  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

       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

       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  sec-
              tion  "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 baseOb-
              ject 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  object-
              Class  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 automati-
              cally assigned ID, instead of being returned by a stored  proce-

       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.  Subse-
              quent 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

       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 normal-
       ized 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 stan-
       dard 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:

         MUST cn
         MAY telephoneNumber $ firstName $ lastName

       To  fetch all values for cn attribute given person ID, we construct the

         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  (telephoneNum-
       ber=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)

       This table defines a mapping between objectclass (its name held in  the
       "name"  column), and a table that holds the primary key for correspond-
       ing 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)
         sel_expr="CONCAT(persons.first_name,' ',persons.last_name)"

       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

       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.

         dn=<dn you choose>
         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 ta-
       ble), which allows you to add any tree structure(s) to your flat  rela-
       tional  data.  Having id of objectclass mapping, we can determine table
       and column for primary key, and keyval stores value of it, thus  defin-
       ing 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 struc-
       tured 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)
                 SELECT 0, UPPER('o=MyCompany,c=NL'),
                     3, 0, 'baseObject' FROM unixusers WHERE userid='root'
                 SELECT (1000000000+userid),
                     1, 0, userid FROM unixusers
                 SELECT (2000000000+groupnummer),
                     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 fil-
       ter 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-explana-
       tory 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:

       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 ta-
       ble.  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 sug-
       gested practice is to define a "referral"  entry  in  ldap_oc_mappings,
       holding  a naming attribute, e.g. "ou" or "cn", a "ref" attribute, con-
       taining 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 replace-
       ment 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 under-
       scores 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

       When the ldap_entry_objclasses table is empty, filters on  the  object-
       Class attribute erroneously result in no candidates.  A workaround con-
       sists in adding at least one row to that table, no matter if  valid  or

       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).

              default slapd configuration file

       See attributes(7) for descriptions of the following attributes:

       |ATTRIBUTE TYPE |       ATTRIBUTE VALUE         |
       |Availability   | service/network/ldap/openldap |
       |Stability      | Pass-through uncommitted      |

       slapd.conf(5), slapd(8).

       Source  code  for open source software components in Oracle Solaris can
       be found at https://www.oracle.com/downloads/opensource/solaris-source-

       This     software     was    built    from    source    available    at
       https://github.com/oracle/solaris-userland.   The  original   community
       source  was downloaded from  ftp://ftp.openldap.org/pub/OpenLDAP/openl-

       Further information about this software can be found on the open source
       community website at http://www.openldap.org/.

OpenLDAP 2.4.57                   2021/01/18                 SLAPD-SQL(5oldap)