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SLAPD-SQL(5)
NAME
slapd-sql - SQL backend to slapd
SYNOPSIS
/usr/internet/openldap/etc/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
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 metainformation 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 metainformation
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 { NO | yes }
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
metainformation, 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 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.
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 people 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.
Typical SQL backend operation
Having metainformation 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 metainformation (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 (referrals, multiclassing etc.)
First of all, let's remember that among other major differences to the
complete LDAP data model, the concept above does not directly support such
things as multiple objectclasses per entry, and referrals. Fortunately,
they are easy to adopt in this scheme. The SQL backend suggests one more
table being added to the schema:
ldap_entry_objectclasses(entry_id,oc_name).
The first contains any number of objectclass names that corresponding
entries will be found by, 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 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
should be replaced by spaces) 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 thru back-
sql, the prettified values are actually used instead.
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
/usr/internet/openldap/etc/slapd.conf
default slapd configuration file
SEE ALSO
slapd.conf(5), slapd(8).
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