dbtoyaml - Database to YAML


dbtoyaml -- extract the schema of a Postgres database in YAML format


dbtoyaml [option...] dbname


dbtoyaml is a utility for extracting the schema of a Postgres database to a YAML formatted specification. By default, the specification is output as a single output stream, which can be redirected or explicitly sent to a file. As an alternative, the --multiple-files option allows you to break down the specification into multiple files, in general, one for each object (see Multiple File Output).

Note that JSON is an official subset of YAML version 1.2, so the dbtoyaml output should also be compatible with JSON tools.

A sample of the output format is as follows:

schema public:
  owner: postgres
  - postgres:
    - all
    - all
  table t1:
        - c2
        expression: (c2 > 123)
    - c1:
        not_null: true
        type: integer
    - c2:
        type: smallint
    - c3:
        default: 'false'
        type: boolean
    - c4:
        type: text
        - c2
          - c21
          schema: s1
          table: t2
    owner: alice
        - c1
schema s1:
  owner: bob
  - bob:
    - all
  - alice:
    - all
  table t2:
    - c21:
         not_null: true
         type: integer
    - c22:
         type: character varying(16)
    owner: bob
        - c21
    - bob:
      - all
    - PUBLIC:
      - select
    - alice:
      - insert:
          grantable: true
      - delete:
          grantable: true
      - update:
          grantable: true
    - carol:
        grantor: alice
        - insert

The above should be mostly self-explanatory. The example database has two tables, named t1 and t2, the first --owned by user 'alice'-- in the public schema and the second --owned by user 'bob'-- in a schema named s1 (also owned by 'bob'). The columns: specifications directly under each table list each column in that table, in the same order as shown by Postgres. The specifications primary_key:, foreign_keys: and check_constraints: define PRIMARY KEY, FOREIGN KEY and CHECK constraints for a given table. Additional specifications (not shown) define unique constraints and indexes.

User 'bob' has granted all privileges to 'alice' on the s1 schema. On table t2, he also granted SELECT to PUBLIC; INSERT, UPDATE and DELETE to 'alice' with GRANT OPTION; and she has in turn granted INSERT to user 'carol'.

dbtoyaml currently supports extracting information about nearly all types of Postgres database objects. See api-ref for a list of supported objects.

The behavior and options of dbtoyaml are patterned after the pg_dump utility since it is most analogous to using pg_dump --schema-only.

Multiple File Output

program: dbtoyaml

The --multiple-files option breaks down the output into multiple files under a given root directory. The root is created if it does not exist. The root directory name defaults to metadata in the system configuration file. The location of the root directory defaults to the configuration item repository.path or can be specified using the --repository option (see config and cmdargs for further details).

The first level contains schema.<name> subdirectories, schema.<name>.yaml files and <objtype>.<name>.yaml files, where <name> is the name of the corresponding objects and <objtype> is the type of top-level (non-schema) object. Note that non-schema refers to Postgres extensions, casts, languages or foreign data wrappers.

The second level, i.e., the schema.<name> subdirectories contain <objtype>.<name>.yaml files for each object in the particular schema (but see below for caveats).

Object Name Conflicts

The names of Postgres objects can include characters that are not allowed in filesystem object names. The most common example is the division operator ('/'), but even table names can include non-alphanumeric characters, if the identifiers are quoted.

In addition, one can define two or more objects with the same base name, e.g., function foo(integer) and function foo(text), or a table named "My Table" and another named "my table" or "MY TABLE". On certain operating systems, i.e., Windows, it is not possible to create two files in the same directory that differ only in the case of their characters.

In order to deal with the aforementioned issues, dbtoyaml places certain objects in common files and transforms object identifiers so that they are suitable for use in files and directories. For example, the information for all user-defined casts are written to the file cast.yaml in the root directory. Functions with the same name but different arguments are written to a single file, e.g., function.foo.yaml in the first example above. Identifiers are also converted to all lowercase, non-alphanumeric characters (excluding underscore) are converted to underscores and, by default, schema object names are truncated to 32 characters.

If two object names, thus transformed, map to the same string, then the objects' information is written to the same file, e.g., table.my_table.yaml in the second example above. If you prefer to change the default truncation length, please define the environment variable PYRSEAS_MAX_IDENT_LEN to some integer value (up to 63).

Version Control and Dropped Objects

It is expected that the output of dbtoyaml --multiple-files will be placed under version control. Further invocations should then update the files in the same directory tree. However, if an object is dropped from the database dbtoyaml would normally only output files for new or changed objects--and thus keep the dropped object file under version control. To deal with dropped objects, dbtoyaml -m outputs a special YAML "index" file, named database.<dbname>.yaml in the root directory. When dbtoyaml -m is run a second time, it looks for this "index" file and if found, proceeds to delete the previous run's .yaml files before outputting new ones.


dbtoyaml accepts the following command-line arguments (in addition to the cmdargs):


Specifies the name of the database whose schema is to be extracted.
cmdoption: -m, --multiple-files
Extracts the schema to a two-level directory tree.  See `Multiple
File Output`_ above.
cmdoption: -n <schema> --schema <schema>
Extracts only a schema matching `schema`. By default, all schemas
are extracted. Multiple schemas can be extracted by using multiple
``-n`` switches. Note that normally all objects that belong to the
schema are extracted as well, unless excluded otherwise.
cmdoption: -N <schema> --exclude-schema <schema>
Does not extract schema matching `schema`.  This can be given more
than once to exclude several schemas.
cmdoption: -O, --no-owner
Do not output object ownership information.  By default, as seen
in the sample output above, database objects (schemas, tables,
etc.) that can be owned by some user, are shown with an "owner:
*username*" element.  The :option:`-O` switch suppresses all those

NOTE: If you specify `--no-owner`, you will most likely also want
to specify :option:`--no-privileges`.  If the former is used
without the latter the resulting YAML output will have privilege
information without user data, which will cause errors if the YAML
is then fed to :doc:`yamltodb`.
cmdoption: -t <table> --table <table>
Extract only tables matching `table`.  Multiple tables can be
extracted by using multiple :option:`-t` switches.  Note that
selecting a table may cause other objects, such as an owned
sequence, to be extracted as well
cmdoption: -T <table> --exclude-table <table>
Do not extract tables matching `table`.  Multiple tables can be
excluded by using multiple :option:`-T` switches.
cmdoption: -x, --no-privileges
Do not output access privilege information.  By default, as seen
in the sample output above, if specific GRANTs have been issued on
various objects (schemas, tables, etc.), the privileges are shown
under each object.  The :option:`-x` switch suppresses all those

See also the NOTE under :option:`--no-owner`.


To extract a database called moviesdb into a file:

dbtoyaml moviesdb > moviesdb.yaml

To extract only the schema named store:

dbtoyaml --schema=store moviesdb > moviesdb.yaml

To extract the tables named film and genre:

dbtoyaml -t film -t genre moviesdb -o moviesdb.yaml

To extract objects, to standard output, except those in schemas product and store:

dbtoyaml -N product -N store moviesdb

To extract objects to a directory under version control:

dbtoyaml moviesdb -m movies/dbspec