[sqlalchemy] Modeling a Tree-looking structure in SqlAlchemy.
hello everyone! I was wondering which is the best way to model a tree-looking structure with SqlAlchemy. Right now, I have this two classes: #!/usr/bin/python2.6 class MyNode(object): def __init__(self): self.items = list() def addItem(self, item): if isinstance(item, MyNode) or isinstance(item, MyLeaf): self.items.append(item) def __str__(self): retval = str() for item in self.items: if isinstance(item, MyNode): retval = retval + \n Node: + str(item) + \n else: retval = \nLeaf: + str(item) + retval return retval class MyLeaf(object): def __init__(self): self.content = I'm a leaf def __str__(self): return self.content As you can see, a node can contain (in its .items list) other nodes, other leafs and a mix of nodes and leafs. When I model that using SqlAlchemy, both MyNode and MyLeaf will be stored their own tables and will have a unique id field in the database. I was wondering if the best thing to do is using two relationships in the MyNode class or trying to do it with one (closer to how it is now). If I use two relationships, the first one (which I could call .otherNodes, for instance) could give me the other instances of MyNode and the second one (.leaves, for instance) would give instances of MyLeaf. And well... I really don't know if it's doable putting both of them together in a unique relationship. I know I'm going to need intermediate tables to model this structure, but I don't know if it's doable (or good idea) to make only one table that may look like: nodes_towards_content = Table( nodes_towards_content, metadata, Column(node_id, Integer, ForeignKey(nodes.id)), Column(other_node_id, Integer, ForeignKey(nodes.id)), Column(other_leaf_id, Integer, ForeignKey(leaves.id)) ) So if I insert a node, the column nodes_to_content.c.other_node_id would take the id of that inserted node while nodes_to_content.c.other_leaf_id would be null, and if I insert a leave, the process would be the opposite. If I use a unique table, I am also a bit concerned of how to retrieve the objects (what to tell the query, I mean). For the moment I have always had relationships that returned one type of objects (or objects that inherited from others), but this would be getting two totally different objects... So if I want to retrieve all the items of a MyNode instance, I don't know what to put in the relationship: class MyNode: [ ... ] def getAllNodes(): items = session.query(?).all() #What to put in ? object, maybe? Thank you in advance! -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalch...@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
[sqlalchemy] Re: How to apply compiler extensions to implement ROW_NUMBER() OVER support for oracle
Hi Michael, this drop-in is great, it does exactly what I need. It just has a small problem in that the variable 'rownum' is not allowed in oracle, it produces a DatabaseError: (DatabaseError) ORA-00923: FROM keyword not found where expected Replacing 'rownum' with 'ora_rn' or something similar fixes this problem. On Dec 9, 5:25 pm, Michael Bayer mike...@zzzcomputing.com wrote: the recipe for built in ROW_NUMBER() for LIMIT/OFFSET should be a drop in and is at: http://www.sqlalchemy.org/trac/wiki/UsageRecipes/WindowFunctionsByDef... applying to certain domain objects only would be a little more involved. You'd probably want to place some kind of hint on the statement that the custom compiler picks up on, or perhaps it looks at the table being selected to make this determination. What would be the safest way to get access to the table/model for which the query was created? I found that element._froms[0] is a pointer to my table, is this a good/stable/portable way to get hold of it? This way I could just instrument my model (aka hint) so see whether I need the ROW_NUMBER approach or not. Ralph -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalch...@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
[sqlalchemy] Inserting Inherited Entities doesn't insert into child table?
Hello,
I'm attempting to user the declarative joined-table inheritance setup
described in the documentation. My classes are as follows
class Relatable(base.Base):
PROFNOTE = 0
__tablename__='relatables'
guid = Column(String(32), primary_key=True)
rel_type = Column('rel_type', SmallInteger, nullable=False)
__mapper_args__ = {'polymorphic_on': type}
def __init__(self, id):
self.guid = id
class ProfNote(relatable.Relatable):
__tablename__ = 'profnotes'
guid = Column('guid', String(32), ForeignKey('relatables.guid'),
nullable=False)
author_id = Column(Integer, ForeignKey('credentials.user_id'),
nullable=False)
title = Column(String(320), nullable=False)
abstract = Column(Text, nullable=False)
published = Column(Boolean, nullable=False)
curriculum = Column(String(320), ForeignKey('curricula.name'),
nullable=False)
__mapper_args__ = { 'polymorphic_identity' :
relatable.Relatable.PROFNOTE }
def __init__(self, guid, title, abstract):
relatable.Relatable.__init__(self, guid)
self.title = title
self.abstract = abstract
self.published = False
I'm trying to insert into the database using the following code:
profnote = ProfNote('...guid...', 'Fake Title', '')
session.add(profnote)
session.commit()
However, insert only occurs into the relatables table. The profnotes
table remains empty. Why is the insert not occurring into the
profnotes table?
Regards,
Ryan
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Re: [sqlalchemy] Inserting Inherited Entities doesn't insert into child table?
profnote doesn't have a primary key. SQLA doesn't emit INSERT for any
primary mapped tables that don't have a PK.
On Dec 13, 2010, at 1:47 PM, rzeigler wrote:
Hello,
I'm attempting to user the declarative joined-table inheritance setup
described in the documentation. My classes are as follows
class Relatable(base.Base):
PROFNOTE = 0
__tablename__='relatables'
guid = Column(String(32), primary_key=True)
rel_type = Column('rel_type', SmallInteger, nullable=False)
__mapper_args__ = {'polymorphic_on': type}
def __init__(self, id):
self.guid = id
class ProfNote(relatable.Relatable):
__tablename__ = 'profnotes'
guid = Column('guid', String(32), ForeignKey('relatables.guid'),
nullable=False)
author_id = Column(Integer, ForeignKey('credentials.user_id'),
nullable=False)
title = Column(String(320), nullable=False)
abstract = Column(Text, nullable=False)
published = Column(Boolean, nullable=False)
curriculum = Column(String(320), ForeignKey('curricula.name'),
nullable=False)
__mapper_args__ = { 'polymorphic_identity' :
relatable.Relatable.PROFNOTE }
def __init__(self, guid, title, abstract):
relatable.Relatable.__init__(self, guid)
self.title = title
self.abstract = abstract
self.published = False
I'm trying to insert into the database using the following code:
profnote = ProfNote('...guid...', 'Fake Title', '')
session.add(profnote)
session.commit()
However, insert only occurs into the relatables table. The profnotes
table remains empty. Why is the insert not occurring into the
profnotes table?
Regards,
Ryan
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[sqlalchemy] Re: Modeling a Tree-looking structure in SqlAlchemy.
I was wondering which is the best way to model a tree-looking structure with SqlAlchemy. I've spent a lot of time dealing with different types of hierarchies in SQLAlchemy lately... One way is to use the nested sets model. This does a decent job at modelling hierarchies, at least as long as you don't have the same leaf in the tree at multiple locations. Some links describing nested sets: http://dev.mysql.com/tech-resources/articles/hierarchical-data.html http://en.wikipedia.org/wiki/Nested_set_model And here is a decent example of how to do this in sqlalchemy: http://www.sqlalchemy.org/trac/browser/examples/adjacency_list/adjacency_list.py The 'classic' way is the 'adjacency list' model. Here is an sqlalchemy example: http://www.sqlalchemy.org/trac/browser/examples/adjacency_list/adjacency_list.py You can also look up another pattern that seems to get labelled as 'materialized path'. No clean sqlalchemy example I know of, but the concept is easy: http://www.google.ca/search?q=(hierarchical+OR+hierarchy)+materialized+path Good luck! Russ -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalch...@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
[sqlalchemy] Re: Modeling a Tree-looking structure in SqlAlchemy.
Sorry, I just saw I messed up the nested sets SQLA example link. Here is the right one: http://www.sqlalchemy.org/trac/browser/examples/nested_sets/nested_sets.py -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalch...@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
[sqlalchemy] Transaction isolation level support?
I'm aware that create_engine() supports an 'isolation_level' argument for setting the transaction isolation level. However - searching the online documentation for isolation_level only gets hits for PostgreSQL and Sqlite, though... http://www.sqlalchemy.org/docs/search.html?q=isolation_level I've checked ahead to the 0.7 docs as well, but still only the two hits. Do other dialects support this, but just not indicate it in the documentation? -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalch...@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
Re: [sqlalchemy] Re: Modeling a Tree-looking structure in SqlAlchemy.
Hello, You should also take a look at http://pypi.python.org/pypi/sqlamp/0.5.2, an implementation of Materialized Path for SQLAlchemy. Regards, Laurent Le 13 déc. 2010 à 23:30, Russell Warren a écrit : Sorry, I just saw I messed up the nested sets SQLA example link. Here is the right one: http://www.sqlalchemy.org/trac/browser/examples/nested_sets/nested_sets.py -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalch...@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en. -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalch...@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
[sqlalchemy] Re: complex mapped collection
On Sep 14, 2010, at 5:03 PM, A.M. wrote:
Hello,
I have a schema like this:
Image
*id
*name
Metadatakey
*id
*exifkey
*name
Metadata
*id
*image_id - Image
*metadatakey_id - Metadatakey
*value
Thanks to Michael Bayer, I was able to put together the image metadata model I
posted on some months ago.
I added an association_proxy to make the db schema more transparent which works
well when reading (as per this example
http://stackoverflow.com/questions/780774/sqlalchemy-dictionary-of-tags), but
when setting an attribute through the association proxy, it seems like I would
need access to the current session to make the determination of whether or not
the metadatakey exists (and grab it).
Is it OK practice to use the session in the _metadataCreator method? Is there a
better way to accomplish this? The last line of the source code below
demonstrates what I wish to accomplish. Thanks.
-M
---
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.types import Integer,Unicode
from sqlalchemy.orm import relationship,scoped_session,backref
from sqlalchemy.orm.session import sessionmaker
from sqlalchemy.schema import Column,ForeignKey
from sqlalchemy.orm.collections import attribute_mapped_collection
from sqlalchemy.engine import create_engine
from sqlalchemy.ext.associationproxy import association_proxy
Base = declarative_base()
class Image(Base):
__tablename__ = 'image'
id = Column(Integer,primary_key=True)
metadatadict = relationship('MetadataValue',
collection_class=attribute_mapped_collection('key'),
primaryjoin='Image.id==MetadataValue.image_id')
def _metadataCreator(key,value):
#--- get existing MetadataName for this key here, but how?
return MetadataValue(namekey=key,value=value)
metadatas =
association_proxy('metadatadict','value',creator=_metadataCreator)
class MetadataName(Base):
__tablename__ = 'metadataname'
id = Column(Integer,primary_key=True)
namekey = Column(Unicode,nullable=False,unique=True)
class MetadataValue(Base):
__tablename__ = 'metadatavalue'
id = Column(Integer,primary_key=True)
image_id = Column(Integer,ForeignKey(Image.id),nullable=False)
image = relationship(Image,
primaryjoin='MetadataValue.image_id==Image.id')
metadataname_id = Column(Integer,ForeignKey(MetadataName.id),nullable=False)
metadataname = relationship(MetadataName,
primaryjoin='MetadataValue.metadataname_id==MetadataName.id')
value = Column(Unicode,nullable=False)
@property
def key(self):
return self.metadataname.namekey
engine = create_engine('postgresql://localhost/test',echo=True)
session = scoped_session(sessionmaker(autocommit=False,bind=engine))
Base.metadata.drop_all(engine)
Base.metadata.create_all(engine)
metadataname1 = MetadataName(namekey=u'MIMEType')
metadataname2 = MetadataName(namekey=u'PixelWidth')
img1 = Image()
metadatavalue1 =
MetadataValue(image=img1,value=u'image/png',metadataname=metadataname1)
session.add_all([metadataname1,img1,metadatavalue1,metadataname2])
session.flush()
#BEGIN TEST AREA
print img1.metadatas['MIMEType']
img1.metadatas['PixelWidth'] = u'300'
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[sqlalchemy] SQLAlchemy / Memcache layer
Hi, I've been attempting to try to add an abstract layer of Memcache on top of the current version of SQLAlchemy, but I've been running into a few different issues and wanted to get a few thoughts on the best approach on loading objects. I've studied the examples at: http://www.sqlalchemy.org/trac/browser/examples/beaker_caching My issue with these methods are they cache simple queries and relationships, but in a fairly simple way and doesn't account for invalidation. They also seem to require more explicit query calls versus some of the sophisticated lazy-loading property relationship mapping of SQLAlchemy. My goal is to add Memcache at the object layer based on primary key (and to control caching of specific object types, versus caching all queries generated). All ColumnProperty's of an object may be stored in cache, and relationships and RelationshipProperty's are ignored for now. The objects that the relationships point to may be stored in cache on their primary key. If an object is updated/deleted, then the object in cache will be invalidated. Basic Example of What I'd Like to Accomplish: # User has property 'image' which has a 'image_id' foreign key relation to Image object # initial request user = Session.query(User).get(1) # checks memcache for user ID 1 # nothing in memcache, queries DB for user ID 1 (image_id for user 1 is 100) # stores user 1 data in memcache image = user.image # checks memcache for image ID 1 # nothing in memcache, queries DB for image ID 100 # stores image 100 data in memcache # separate subsequent request user = Session.query(User).get(1) # checks memcache for user ID 1, found it! # populate User object with data from memcache image = user.image # checks memcache for image ID 100, found it! # populate Image object with data from memcache image.view_count = image.view_count + 1 Session.commit() # invalidate image ID 100 in memcache I suspect the best way to issue invalidate requests to Memcache will be to create a MapperExtension and use before_update() and before_delete(). However, I'm having much more trouble figuring out where and how I should store data in Memcache and when/how to load from it. MapperExtensions only offer hooks after data has been read from the DB. I've looked into subclassing the Query class and overriding the get() function (as well as a few other functions), but the problem I run into is that I can load the regular columns properties, but will run into issues with lazy-loaded RelationshipProperties with mostly the error: DetachedInstanceError: Parent instance User at 0x7fc7503942d0 is not bound to a Session; lazy load operation of attribute 'images' cannot proceed Any ideas or suggestions? Thanks, Vince -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalch...@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
Re: [sqlalchemy] Re: How to apply compiler extensions to implement ROW_NUMBER() OVER support for oracle
On Dec 13, 2010, at 12:12 PM, Ralph Heinkel wrote: Hi Michael, this drop-in is great, it does exactly what I need. It just has a small problem in that the variable 'rownum' is not allowed in oracle, it produces a DatabaseError: (DatabaseError) ORA-00923: FROM keyword not found where expected Replacing 'rownum' with 'ora_rn' or something similar fixes this problem. On Dec 9, 5:25 pm, Michael Bayer mike...@zzzcomputing.com wrote: the recipe for built in ROW_NUMBER() for LIMIT/OFFSET should be a drop in and is at: http://www.sqlalchemy.org/trac/wiki/UsageRecipes/WindowFunctionsByDef... applying to certain domain objects only would be a little more involved. You'd probably want to place some kind of hint on the statement that the custom compiler picks up on, or perhaps it looks at the table being selected to make this determination. What would be the safest way to get access to the table/model for which the query was created? I found that element._froms[0] is a pointer to my table, is this a good/stable/portable way to get hold of it? This way I could just instrument my model (aka hint) so see whether I need the ROW_NUMBER approach or not. Theres different ways to locate tables in the selectable depending on what you want. In this case it might be best for you to look at the _order_by_clause attribute to see which tables or selectables are being ordered upon, since those are the columns/tables that are impacted by the ROW NUMBER operation. select() itself has a public froms member as well. This member includes all FROM clauses including those that might not render if the select is embedded within another one where correlation is taking place - if you wanted to filter more carefully like that I'd emulate what compiler.py:SQLCompiler.visit_select() is doing. Ralph -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalch...@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en. -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalch...@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
Re: [sqlalchemy] SQLAlchemy / Memcache layer
On Dec 13, 2010, at 8:31 PM, Vince Ng wrote:
Hi,
I've been attempting to try to add an abstract layer of Memcache on top of
the current version of SQLAlchemy, but I've been running into a few different
issues and wanted to get a few thoughts on the best approach on loading
objects.
I've studied the examples at:
http://www.sqlalchemy.org/trac/browser/examples/beaker_caching
My issue with these methods are they cache simple queries and relationships,
but in a fairly simple way and doesn't account for invalidation. They also
seem to require more explicit query calls versus some of the sophisticated
lazy-loading property relationship mapping of SQLAlchemy.
My goal is to add Memcache at the object layer based on primary key (and to
control caching of specific object types, versus caching all queries
generated). All ColumnProperty's of an object may be stored in cache, and
relationships and RelationshipProperty's are ignored for now. The objects
that the relationships point to may be stored in cache on their primary key.
If an object is updated/deleted, then the object in cache will be invalidated.
Basic Example of What I'd Like to Accomplish:
# User has property 'image' which has a 'image_id' foreign key relation
to Image object
# initial request
user = Session.query(User).get(1)
# checks memcache for user ID 1
# nothing in memcache, queries DB for user ID 1 (image_id for
user 1 is 100)
# stores user 1 data in memcache
image = user.image
# checks memcache for image ID 1
# nothing in memcache, queries DB for image ID 100
# stores image 100 data in memcache
# separate subsequent request
user = Session.query(User).get(1)
# checks memcache for user ID 1, found it!
# populate User object with data from memcache
image = user.image
# checks memcache for image ID 100, found it!
# populate Image object with data from memcache
image.view_count = image.view_count + 1
Session.commit()
# invalidate image ID 100 in memcache
I suspect the best way to issue invalidate requests to Memcache will be to
create a MapperExtension and use before_update() and before_delete().
I'd go with SessionExtension instead - you can gather up everything from the
dirty list in one go and invalidate.
However, I'm having much more trouble figuring out where and how I should
store data in Memcache and when/how to load from it.
if you're going for get(), subclass Query and override get() to check memcache
first. This is pretty much what LOLApps! talked about in their Pycon talk
last year. But this approach is not as comprehensive as that of the Beaker
example, which places itself at the central point of __iter__() and can make
decisions about all queries, including that it can cache results not just on
primary key but on filter criterion too.
The loading of related many-to-ones like user.image uses part of the
functionality of query.get(), but not the get() method itself, so again
overriding __iter__() as stated in the example is the most focused place. The
Beaker example illustrates how to augment exactly the process of the
many-to-one lazyload, using custom query options that are invoked at the point
of load. The RelationshipCache() represents an object that, when placed in the
options collection of a Query, is invoked directly before the lazyload
occurs. It looks at the path that is to be loaded, of the form (mapper,
attributename), i.e. such as (user_mapper, 'image'), then compares this path
into its own list of paths to determine if the Query should be instructed to
pull from cache. You can modify this to do something like
user_mapper.get_property('image').direction is
sqlalchemy.orm.interfaces.MANYTOONE to apply caching to all m2os. Running
the Beaker example for a few hours and using pdb to step through each line of
code should make it clearer what's going on.
MapperExtensions only offer hooks after data has been read from the DB. I've
looked into subclassing the Query class and overriding the get() function (as
well as a few other functions), but the problem I run into is that I can load
the regular columns properties, but will run into issues with lazy-loaded
RelationshipProperties with mostly the error:
DetachedInstanceError: Parent instance User at 0x7fc7503942d0 is not bound
to a Session; lazy load operation of attribute 'images' cannot proceed
You need your objects to be bound to Sessions when they load things - this so
they are aware of the database transaction they mean to participate in, as well
as where they should be loading unloaded (or in this case, cache-expired as
well) data. The Beaker example uses query.merge_result() for all loaded
results to ensure that objects returned participate
[sqlalchemy] Re: Transaction isolation level support?
Do other dialects support this, but just not indicate it in the documentation? On further investigation I see this old ticket: http://www.sqlalchemy.org/trac/ticket/443 ... which implies it is, in fact, only for PostgreSQL and Sqlite at the moment. I'm also quite interested in setting the isolation level on a per session/connection basis. However - it seems like the isolation_level argument to create_engine() sets the isolation level for all managed connections. I recognize that there may (at least) be some issues with this based on the connection pooling scheme in use, but is there a way (even a hack) to do a one-time set of the isolation level to SERIALIZABLE (for example) for a created session? This thread makes it seem like per-session/connection isolation setting is not as simple as it might seem at first... http://groups.google.com/group/sqlalchemy-devel/browse_thread/thread/653b6b2f49a940b8 And this StackOverflow question makes it seem like it isn't easy to set the isolation level per session... http://bit.ly/eG5DUl Still digging... Russ -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalch...@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
[sqlalchemy] UserDefinedType for tuples
I want to make a custom type and I'm not sure whether to use UserDefinedType or TypeDecorator. for a UserDefinedType it seems I must write bind_processor and result_processor or for TypeDecorator it seems I must write process_bind_param and process_result_value I think I need a UserDefinedType as I'm combining two primitive types rather than specialising one. I want Vector2D(float, float) and an ordered list of such vectors and to pass these into the DB using something as close as possible to Python such as [(ax, ay), (bx, by), (cx, cy)] After reading some doco and posts I'm still unclear exactly what the functions I have to write should do as they often seem to do very little. Really, I just want to insert tuples into columns. -- You received this message because you are subscribed to the Google Groups sqlalchemy group. To post to this group, send email to sqlalch...@googlegroups.com. To unsubscribe from this group, send email to sqlalchemy+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/sqlalchemy?hl=en.
