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Dumping Content to Disk

Substance D’s object database stores native Python representations of resources. This is easy enough to work with: you can run bin/pshell to get an interactive prompt, write longer ad-hoc console scripts, or just put code into your application.

However, production sites usually want exportable representations of important data stored in a long-term format. For this, Substance D provides a dump facility for content types to be serialized in a YAML representation on disk.


You’ll note in the following the absence of docs on loading data. This is intentional. The process of loading data into a new, or semi-new, or newer-than-new site has many policy implications. Too many to fit into a single loading script. Substance D considers the particulars of loading data to be in the province of the application developer.

Dumping Resources Using sd_dump

The sd_dump console script loads your Substance D application, connects to your object database, and writes serialized representations of resources to disk in a directory hierarchy:

$ ../bin/sd_dump --help
Usage: sd_dump [options]

 Dump an object (and its subobjects) to the filesystem:  sd_dump [--source
=ZODB-PATH] [--dest=FILESYSTEM-PATH] config_uri   Dumps the object at ZODB-
PATH and all of its subobjects to a   filesystem path.  Such a dump can be
loaded (programmatically)   by using the substanced.dump.load function  e.g.
sd_dump --source=/ --dest=/my/dump etc/development.ini

  -h, --help            show this help message and exit
  -s ZODB-PATH, --source=ZODB-PATH
                        The ZODB source path to dump (e.g. /foo/bar or /)
                        The destination filesystem path to dump to.

For example:

$ ../bin/sd_dump ../etc/development.ini
2013-01-07 13:27:03,939 INFO  [ZEO.ClientStorage][MainThread] ('localhost', 9963) ClientStorage (pid=93148) created RW/normal for storage: 'main'
2013-01-07 13:27:03,941 INFO  [ZEO.cache][MainThread] created temporary cache file '<fdopen>'
2013-01-07 13:27:03,981 WARNI [ZEO.zrpc][Connect([(2, ('localhost', 9963))])] (93148) CW: error connecting to ('fe80::1%lo0', 9963): EHOSTUNREACH
2013-01-07 13:27:03,982 WARNI [ZEO.zrpc][Connect([(2, ('localhost', 9963))])] (93148) CW: error connecting to ('fe80::1%lo0', 9963): EHOSTUNREACH
2013-01-07 13:27:04,002 WARNI [ZEO.zrpc][Connect([(2, ('localhost', 9963))])] (93148) CW: error connecting to ('::1', 9963): EINVAL
2013-01-07 13:27:04,003 INFO  [ZEO.ClientStorage][Connect([(2, ('localhost', 9963))])] ('localhost', 9963) Testing connection <ManagedClientConnection ('', 9963)>
2013-01-07 13:27:04,004 INFO  [ZEO.zrpc.Connection(C)][('localhost', 9963) zeo client networking thread] ( received handshake 'Z3101'
2013-01-07 13:27:04,105 INFO  [ZEO.ClientStorage][Connect([(2, ('localhost', 9963))])] ('localhost', 9963) Server authentication protocol None
2013-01-07 13:27:04,106 INFO  [ZEO.ClientStorage][Connect([(2, ('localhost', 9963))])] ('localhost', 9963) Connected to storage: ('localhost', 9963)
2013-01-07 13:27:04,108 INFO  [ZEO.ClientStorage][Connect([(2, ('localhost', 9963))])] ('localhost', 9963) No verification necessary -- empty cache
2013-01-07 13:27:04,727 INFO  [substanced.catalog][MainThread] system update_indexes: no indexes added or removed
2013-01-07 13:27:04,730 INFO  [substanced.catalog][MainThread] sdidemo update_indexes: no indexes added or removed
2013-01-07 13:27:04,732 INFO  [substanced.dump][MainThread] Dumping /
2013-01-07 13:27:04,749 INFO  [substanced.dump][MainThread] Dumping /principals
2013-01-07 13:27:04,754 INFO  [substanced.dump][MainThread] Dumping /principals/users
2013-01-07 13:27:04,760 INFO  [substanced.dump][MainThread] Dumping /principals/users/admin
2013-01-07 13:27:04,779 INFO  [substanced.dump][MainThread] Dumping /principals/resets
2013-01-07 13:27:04,783 INFO  [substanced.dump][MainThread] Dumping /principals/groups

…with logging messages being emitted until all known content is dumped. A dump subdirectory in the current directory is created (if no argument is provided) containing:

$ ls
acl.yaml    propsheets      references.yaml resource.yaml   resources


To correctly encode as much meaning as possible, the dump files contain some advanced and custom YAML constructs when needed.

acl.yaml For Security Settings

This YAML file contains security settings for this resource. For example:

- !!python/tuple [Allow, 1644064392535565429, !all_permissions '']

references.yaml for Reference Information

Data about references aren’t stored on the resources involved in the reference. Instead, they are stored in the objectmap. This file contains the reference information for the resource identified at the current dump directory. For example:

!interface 'substanced.interfaces.PrincipalToACLBearing':
  sources: [1644064392535565429]

workflow.yaml for Workflow Settings

The workflow engine can contain information about resource state. For example:

data: {document: draft}

propsheets Directory for Property Sheet Data

Resources can have multiple system-defined or application-defined property sheets on resources. These are serialized as subdirectories under propsheets, with a directory for each property sheet. For example, a resources propsheets/Basic/properties.yaml might contain:

{body: !!python/unicode 'The quick brown fox jumps over the lazy dog. The quick brown
    fox jumps over the lazy dog.  The quick brown fox jumps over the lazy dog.
    The quick brown fox jumps over the lazy dog. The quick brown fox jumps over the
    lazy dog. The quick brown fox jumps over the lazy dog. The quick brown fox jumps
    over the lazy dog. The quick brown fox jumps over the lazy dog. The quick brown
    fox jumps over the lazy dog. ', name: !!python/unicode 'document_0', title: !!python/unicode 'Document
    0 Binder 0'}

resource.yaml for Content Type Information

Each directory after the top corresponds to a resource in the database. As such, the resource likely has content type information. The dump script encodes this into a YAML file in the resource’s dump directory:

{content_type: Root, created: !!timestamp '2013-01-07 14:23:23.133436', is_service: false,
  name: null, oid: 1644064392535565415}

resources for Contained Resources in Containers

If the resource at a current dump directory is a Folder or some other kind of container, it will contain a resources subdirectory. This might contain more subfolders and thus subdirectories. It might also contain individual resources, as a subdirectory named with the resource name.

Custom Dumping with __dump__

The built-in facilities allow automatic dumping of most information for your content, including information in your property sheets, the content type, security settings, references, workflows, etc.

If you do need extra information dumped to YAML about your content type, Substance D has a Python protocol using an __dump__ on your @content class. As an example, :py:meth:substanced.principal.User.dump is a callable which returns a mapping of simple Python objects. The dumper checks to see if a resource has a __dump__ method. If so, it calls the method, encodes the result to YAML, and writes it to an adhoc.yaml file in the dumped-resource’s directory.

The inverse is also true. If a content type has a __load__ method, information from that method is added to the state that is loaded.

Adding New Dumpers

The adhoc.yaml file that we just saw is an example of the AdhocAttrDumper. There are seven other dumpers built-in: acl, workflow, references, sdiproperties, interfaces, order, and propsheets.

If you would like a custom dumper, you can register it with config.add_dumper. For example, substanced.dump.includeme() registers the existing dumpers and their dumper factories:

def includeme(config):
        ('acl', ACLDumper),
        ('workflow', WorkflowDumper),
        ('references', ReferencesDumper),
        ('sdiproperties', SDIPropertiesDumper),
        ('interfaces', DirectlyProvidedInterfacesDumper),
        ('order', FolderOrderDumper),
        ('propsheets', PropertySheetDumper),
        ('adhoc', AdhocAttrDumper),
    config.add_directive('add_dumper', add_dumper)
    for dumper_name, dumper_factory in DEFAULT_DUMPERS:
        config.add_dumper(dumper_name, dumper_factory)