diff --git a/swh/model/model.py b/swh/model/model.py
index 512824d..26accb6 100644
--- a/swh/model/model.py
+++ b/swh/model/model.py
@@ -1,470 +1,474 @@
 # Copyright (C) 2018-2019 The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
 
 import datetime
 
 from abc import ABCMeta, abstractmethod
 from enum import Enum
 from typing import List, Optional, Dict
 
 import attr
 import dateutil.parser
 
 from .identifiers import (
     normalize_timestamp, directory_identifier, revision_identifier,
     release_identifier, snapshot_identifier
 )
 from .hashutil import DEFAULT_ALGORITHMS, hash_to_bytes
 
 SHA1_SIZE = 20
 
 # TODO: Limit this to 20 bytes
 Sha1Git = bytes
 
 
 class BaseModel:
     """Base class for SWH model classes.
 
     Provides serialization/deserialization to/from Python dictionaries,
     that are suitable for JSON/msgpack-like formats."""
 
     def to_dict(self):
         """Wrapper of `attr.asdict` that can be overridden by subclasses
         that have special handling of some of the fields."""
 
         def dictify(value):
             if isinstance(value, BaseModel):
                 return value.to_dict()
             elif isinstance(value, Enum):
                 return value.value
             elif isinstance(value, dict):
                 return {k: dictify(v) for k, v in value.items()}
             elif isinstance(value, list):
                 return [dictify(v) for v in value]
             else:
                 return value
 
         ret = attr.asdict(self, recurse=False)
         return dictify(ret)
 
     @classmethod
     def from_dict(cls, d):
         """Takes a dictionary representing a tree of SWH objects, and
         recursively builds the corresponding objects."""
         return cls(**d)
 
 
 class HashableObject(metaclass=ABCMeta):
     """Mixin to automatically compute object identifier hash when
     the associated model is instantiated."""
 
     @staticmethod
     @abstractmethod
     def compute_hash(object_dict):
         """Derived model classes must implement this to compute
         the object hash from its dict representation."""
         pass
 
     def __attrs_post_init__(self):
         if not self.id:
             obj_id = hash_to_bytes(self.compute_hash(self.to_dict()))
             object.__setattr__(self, 'id', obj_id)
 
 
 @attr.s(frozen=True)
 class Person(BaseModel):
     """Represents the author/committer of a revision or release."""
     name = attr.ib(type=bytes)
     email = attr.ib(type=bytes)
     fullname = attr.ib(type=bytes)
 
 
 @attr.s(frozen=True)
 class Timestamp(BaseModel):
     """Represents a naive timestamp from a VCS."""
     seconds = attr.ib(type=int)
     microseconds = attr.ib(type=int)
 
     @seconds.validator
     def check_seconds(self, attribute, value):
         """Check that seconds fit in a 64-bits signed integer."""
         if not (-2**63 <= value < 2**63):
             raise ValueError('Seconds must be a signed 64-bits integer.')
 
     @microseconds.validator
     def check_microseconds(self, attribute, value):
         """Checks that microseconds are positive and < 1000000."""
         if not (0 <= value < 10**6):
             raise ValueError('Microseconds must be in [0, 1000000[.')
 
 
 @attr.s(frozen=True)
 class TimestampWithTimezone(BaseModel):
     """Represents a TZ-aware timestamp from a VCS."""
     timestamp = attr.ib(type=Timestamp)
     offset = attr.ib(type=int)
     negative_utc = attr.ib(type=bool)
 
     @offset.validator
     def check_offset(self, attribute, value):
         """Checks the offset is a 16-bits signed integer (in theory, it
         should always be between -14 and +14 hours)."""
         if not (-2**15 <= value < 2**15):
             # max 14 hours offset in theory, but you never know what
             # you'll find in the wild...
             raise ValueError('offset too large: %d minutes' % value)
 
     @classmethod
     def from_dict(cls, d):
         """Builds a TimestampWithTimezone from any of the formats
         accepted by :func:`swh.model.normalize_timestamp`."""
         d = normalize_timestamp(d)
         return cls(
             timestamp=Timestamp.from_dict(d['timestamp']),
             offset=d['offset'],
             negative_utc=d['negative_utc'])
 
 
 @attr.s(frozen=True)
 class Origin(BaseModel):
     """Represents a software source: a VCS and an URL."""
     url = attr.ib(type=str)
     type = attr.ib(type=Optional[str], default=None)
 
     def to_dict(self):
         r = super().to_dict()
         r.pop('type', None)
         return r
 
 
 @attr.s(frozen=True)
 class OriginVisit(BaseModel):
     """Represents a visit of an origin at a given point in time, by a
     SWH loader."""
     origin = attr.ib(type=str)
     date = attr.ib(type=datetime.datetime)
     status = attr.ib(
         type=str,
         validator=attr.validators.in_(['ongoing', 'full', 'partial']))
     type = attr.ib(type=str)
     snapshot = attr.ib(type=Optional[Sha1Git])
     metadata = attr.ib(type=Optional[Dict[str, object]],
                        default=None)
 
     visit = attr.ib(type=Optional[int],
                     default=None)
     """Should not be set before calling 'origin_visit_add()'."""
 
     def to_dict(self):
         """Serializes the date as a string and omits the visit id if it is
         `None`."""
         ov = super().to_dict()
         if ov['visit'] is None:
             del ov['visit']
         return ov
 
     @classmethod
     def from_dict(cls, d):
         """Parses the date from a string, and accepts missing visit ids."""
         d = d.copy()
         date = d.pop('date')
         return cls(
             date=(date
                   if isinstance(date, datetime.datetime)
                   else dateutil.parser.parse(date)),
             **d)
 
 
 class TargetType(Enum):
     """The type of content pointed to by a snapshot branch. Usually a
     revision or an alias."""
     CONTENT = 'content'
     DIRECTORY = 'directory'
     REVISION = 'revision'
     RELEASE = 'release'
     SNAPSHOT = 'snapshot'
     ALIAS = 'alias'
 
 
 class ObjectType(Enum):
     """The type of content pointed to by a release. Usually a revision"""
     CONTENT = 'content'
     DIRECTORY = 'directory'
     REVISION = 'revision'
     RELEASE = 'release'
     SNAPSHOT = 'snapshot'
 
 
 @attr.s(frozen=True)
 class SnapshotBranch(BaseModel):
     """Represents one of the branches of a snapshot."""
     target = attr.ib(type=bytes)
     target_type = attr.ib(type=TargetType)
 
     @target.validator
     def check_target(self, attribute, value):
         """Checks the target type is not an alias, checks the target is a
         valid sha1_git."""
         if self.target_type != TargetType.ALIAS and self.target is not None:
             if len(value) != 20:
                 raise ValueError('Wrong length for bytes identifier: %d' %
                                  len(value))
 
     @classmethod
     def from_dict(cls, d):
         return cls(
             target=d['target'],
             target_type=TargetType(d['target_type']))
 
 
 @attr.s(frozen=True)
 class Snapshot(BaseModel, HashableObject):
     """Represents the full state of an origin at a given point in time."""
     branches = attr.ib(type=Dict[bytes, Optional[SnapshotBranch]])
     id = attr.ib(type=Sha1Git, default=b'')
 
     @staticmethod
     def compute_hash(object_dict):
         return snapshot_identifier(object_dict)
 
     @classmethod
     def from_dict(cls, d):
         d = d.copy()
         return cls(
             branches={
                 name: SnapshotBranch.from_dict(branch) if branch else None
                 for (name, branch) in d.pop('branches').items()
             },
             **d)
 
 
 @attr.s(frozen=True)
 class Release(BaseModel, HashableObject):
     name = attr.ib(type=bytes)
     message = attr.ib(type=bytes)
     target = attr.ib(type=Optional[Sha1Git])
     target_type = attr.ib(type=ObjectType)
     synthetic = attr.ib(type=bool)
     author = attr.ib(type=Optional[Person],
                      default=None)
     date = attr.ib(type=Optional[TimestampWithTimezone],
                    default=None)
     metadata = attr.ib(type=Optional[Dict[str, object]],
                        default=None)
     id = attr.ib(type=Sha1Git, default=b'')
 
     @staticmethod
     def compute_hash(object_dict):
         return release_identifier(object_dict)
 
     @author.validator
     def check_author(self, attribute, value):
         """If the author is `None`, checks the date is `None` too."""
         if self.author is None and self.date is not None:
             raise ValueError('release date must be None if author is None.')
 
     def to_dict(self):
         rel = super().to_dict()
         if rel['metadata'] is None:
             del rel['metadata']
         return rel
 
     @classmethod
     def from_dict(cls, d):
         d = d.copy()
         if d.get('author'):
             d['author'] = Person.from_dict(d['author'])
         if d.get('date'):
             d['date'] = TimestampWithTimezone.from_dict(d['date'])
         return cls(
             target_type=ObjectType(d.pop('target_type')),
             **d)
 
 
 class RevisionType(Enum):
     GIT = 'git'
     TAR = 'tar'
     DSC = 'dsc'
     SUBVERSION = 'svn'
     MERCURIAL = 'hg'
 
 
 @attr.s(frozen=True)
 class Revision(BaseModel, HashableObject):
     message = attr.ib(type=bytes)
     author = attr.ib(type=Person)
     committer = attr.ib(type=Person)
     date = attr.ib(type=Optional[TimestampWithTimezone])
     committer_date = attr.ib(type=Optional[TimestampWithTimezone])
     type = attr.ib(type=RevisionType)
     directory = attr.ib(type=Sha1Git)
     synthetic = attr.ib(type=bool)
     metadata = attr.ib(type=Optional[Dict[str, object]],
                        default=None)
     parents = attr.ib(type=List[Sha1Git],
                       default=attr.Factory(list))
     id = attr.ib(type=Sha1Git, default=b'')
 
     @staticmethod
     def compute_hash(object_dict):
         return revision_identifier(object_dict)
 
     @classmethod
     def from_dict(cls, d):
         d = d.copy()
         date = d.pop('date')
         if date:
             date = TimestampWithTimezone.from_dict(date)
 
         committer_date = d.pop('committer_date')
         if committer_date:
             committer_date = TimestampWithTimezone.from_dict(
                 committer_date)
 
         return cls(
             author=Person.from_dict(d.pop('author')),
             committer=Person.from_dict(d.pop('committer')),
             date=date,
             committer_date=committer_date,
             type=RevisionType(d.pop('type')),
             **d)
 
 
 @attr.s(frozen=True)
 class DirectoryEntry(BaseModel):
     name = attr.ib(type=bytes)
     type = attr.ib(type=str,
                    validator=attr.validators.in_(['file', 'dir', 'rev']))
     target = attr.ib(type=Sha1Git)
     perms = attr.ib(type=int)
     """Usually one of the values of `swh.model.from_disk.DentryPerms`."""
 
 
 @attr.s(frozen=True)
 class Directory(BaseModel, HashableObject):
     entries = attr.ib(type=List[DirectoryEntry])
     id = attr.ib(type=Sha1Git, default=b'')
 
     @staticmethod
     def compute_hash(object_dict):
         return directory_identifier(object_dict)
 
     @classmethod
     def from_dict(cls, d):
         d = d.copy()
         return cls(
             entries=[DirectoryEntry.from_dict(entry)
                      for entry in d.pop('entries')],
             **d)
 
 
 @attr.s(frozen=True)
 class BaseContent(BaseModel):
     def to_dict(self):
         content = super().to_dict()
         if content['ctime'] is None:
             del content['ctime']
         return content
 
     @classmethod
     def from_dict(cls, d, use_subclass=True):
         if use_subclass:
             # Chooses a subclass to instantiate instead.
             if d['status'] == 'absent':
                 return SkippedContent.from_dict(d)
             else:
                 return Content.from_dict(d)
         else:
             return super().from_dict(d)
 
     def get_hash(self, hash_name):
         if hash_name not in DEFAULT_ALGORITHMS:
             raise ValueError('{} is not a valid hash name.'.format(hash_name))
         return getattr(self, hash_name)
 
+    def hashes(self) -> Dict[str, bytes]:
+        """Returns a dictionary {hash_name: hash_value}"""
+        return {algo: getattr(self, algo) for algo in DEFAULT_ALGORITHMS}
+
 
 @attr.s(frozen=True)
 class Content(BaseContent):
     sha1 = attr.ib(type=bytes)
     sha1_git = attr.ib(type=Sha1Git)
     sha256 = attr.ib(type=bytes)
     blake2s256 = attr.ib(type=bytes)
 
     length = attr.ib(type=int)
 
     status = attr.ib(
         type=str,
         default='visible',
         validator=attr.validators.in_(['visible', 'hidden']))
     data = attr.ib(type=Optional[bytes],
                    default=None)
 
     ctime = attr.ib(type=Optional[datetime.datetime],
                     default=None)
 
     @length.validator
     def check_length(self, attribute, value):
         """Checks the length is positive."""
         if value < 0:
             raise ValueError('Length must be positive.')
 
     def to_dict(self):
         content = super().to_dict()
         if content['data'] is None:
             del content['data']
         return content
 
     @classmethod
     def from_dict(cls, d):
         return super().from_dict(d, use_subclass=False)
 
 
 @attr.s(frozen=True)
 class SkippedContent(BaseContent):
     sha1 = attr.ib(type=Optional[bytes])
     sha1_git = attr.ib(type=Optional[Sha1Git])
     sha256 = attr.ib(type=Optional[bytes])
     blake2s256 = attr.ib(type=Optional[bytes])
 
     length = attr.ib(type=int)
 
     status = attr.ib(
         type=str,
         validator=attr.validators.in_(['absent']))
     reason = attr.ib(type=Optional[str],
                      default=None)
 
     origin = attr.ib(type=Optional[Origin],
                      default=None)
 
     ctime = attr.ib(type=Optional[datetime.datetime],
                     default=None)
 
     @reason.validator
     def check_reason(self, attribute, value):
         """Checks the reason is full if status != absent."""
         assert self.reason == value
         if value is None:
             raise ValueError('Must provide a reason if content is absent.')
 
     @length.validator
     def check_length(self, attribute, value):
         """Checks the length is positive or -1."""
         if value < -1:
             raise ValueError('Length must be positive or -1.')
 
     def to_dict(self):
         content = super().to_dict()
         if content['origin'] is None:
             del content['origin']
         return content
 
     @classmethod
     def from_dict(cls, d):
         d2 = d
         d = d.copy()
         if d.pop('data', None) is not None:
             raise ValueError('SkippedContent has no "data" attribute %r' % d2)
         return super().from_dict(d, use_subclass=False)
diff --git a/swh/model/tests/test_model.py b/swh/model/tests/test_model.py
index 5560127..e905725 100644
--- a/swh/model/tests/test_model.py
+++ b/swh/model/tests/test_model.py
@@ -1,114 +1,121 @@
 # Copyright (C) 2019 The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
 
 import copy
 
 from hypothesis import given
 
 from swh.model.model import Content, Directory, Revision, Release, Snapshot
 from swh.model.hashutil import hash_to_bytes
 from swh.model.hypothesis_strategies import objects, origins, origin_visits
 from swh.model.identifiers import (
     directory_identifier, revision_identifier, release_identifier,
     snapshot_identifier
 )
 from swh.model.tests.test_identifiers import (
     directory_example, revision_example, release_example, snapshot_example
 )
 
 
 @given(objects())
 def test_todict_inverse_fromdict(objtype_and_obj):
     (obj_type, obj) = objtype_and_obj
 
     if obj_type in ('origin', 'origin_visit'):
         return
 
     obj_as_dict = obj.to_dict()
     obj_as_dict_copy = copy.deepcopy(obj_as_dict)
 
     # Check the composition of to_dict and from_dict is the identity
     assert obj == type(obj).from_dict(obj_as_dict)
 
     # Check from_dict() does not change the input dict
     assert obj_as_dict == obj_as_dict_copy
 
     # Check the composition of from_dict and to_dict is the identity
     assert obj_as_dict == type(obj).from_dict(obj_as_dict).to_dict()
 
 
 @given(origins())
 def test_todict_origins(origin):
     obj = origin.to_dict()
 
     assert 'type' not in obj
     assert type(origin)(url=origin.url) == type(origin).from_dict(obj)
 
 
 @given(origin_visits())
 def test_todict_origin_visits(origin_visit):
     obj = origin_visit.to_dict()
 
     assert origin_visit == type(origin_visit).from_dict(obj)
 
 
 def test_content_get_hash():
     hashes = dict(
         sha1=b'foo', sha1_git=b'bar', sha256=b'baz', blake2s256=b'qux')
     c = Content(length=42, status='visible', **hashes)
     for (hash_name, hash_) in hashes.items():
         assert c.get_hash(hash_name) == hash_
 
 
+def test_content_hashes():
+    hashes = dict(
+        sha1=b'foo', sha1_git=b'bar', sha256=b'baz', blake2s256=b'qux')
+    c = Content(length=42, status='visible', **hashes)
+    assert c.hashes() == hashes
+
+
 def test_directory_model_id_computation():
     dir_dict = dict(directory_example)
     del dir_dict['id']
 
     dir_id = hash_to_bytes(directory_identifier(dir_dict))
     for dir_model in [Directory(**dir_dict), Directory.from_dict(dir_dict)]:
         assert dir_model.id == dir_id
 
 
 def test_revision_model_id_computation():
     rev_dict = dict(revision_example)
     del rev_dict['id']
 
     rev_id = hash_to_bytes(revision_identifier(rev_dict))
     for rev_model in [Revision(**rev_dict), Revision.from_dict(rev_dict)]:
         assert rev_model.id == rev_id
 
 
 def test_revision_model_id_computation_with_no_date():
     """We can have revision with date to None
 
     """
     rev_dict = dict(revision_example)
     rev_dict['date'] = None
     rev_dict['committer_date'] = None
     del rev_dict['id']
 
     rev_id = hash_to_bytes(revision_identifier(rev_dict))
     for rev_model in [Revision(**rev_dict), Revision.from_dict(rev_dict)]:
         assert rev_model.date is None
         assert rev_model.committer_date is None
         assert rev_model.id == rev_id
 
 
 def test_release_model_id_computation():
     rel_dict = dict(release_example)
     del rel_dict['id']
 
     rel_id = hash_to_bytes(release_identifier(rel_dict))
     for rel_model in [Release(**rel_dict), Release.from_dict(rel_dict)]:
         assert rel_model.id == hash_to_bytes(rel_id)
 
 
 def test_snapshot_model_id_computation():
     snp_dict = dict(snapshot_example)
     del snp_dict['id']
 
     snp_id = hash_to_bytes(snapshot_identifier(snp_dict))
     for snp_model in [Snapshot(**snp_dict), Snapshot.from_dict(snp_dict)]:
         assert snp_model.id == snp_id