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       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                (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


       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,
              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


       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

       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
              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

       fetch_attrs <attrlist>
       fetch_all_attrs { NO | yes }
              The  first statement allows 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


       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
       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:

         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

       for telephoneNumber we can use:

         SELECT AS telephoneNumber FROM persons,phones
             WHERE AND

       If   we   wanted   to   service   LDAP   requests   with  filters  like
       (telephoneNumber=123*), we would construct something like:

         SELECT ... FROM persons,phones
                 AND 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
       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
       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
       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)
                 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,, 'person' AS objectClass,
                ldap_entries.dn AS dn
           FROM ldap_entries,persons,phones
            AND ldap_entries.objclass=?
            AND ldap_entries.parent=?
            AND ( 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 AS telephoneNumber
           FROM persons,phones
          WHERE AND

       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:

       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


       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).


              default slapd configuration file


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