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• Backup, Migrate or Clone Failing CentOS 4 (LVM)

  - by Hegelworm

  I've been running a BlueQuartz CentOS 4 system (Nuonce.net distro) for a few years now and although the hard drive (Deskstar) has always been a bit noisy, on a few recent occasions I've heard it having trouble spinning up. Basically, I want to clone this drive to a similar sized one (80 Gig). I've spent many hours reading upon dd, dd_rescue, rsync, clonezilla and LVM mirroring yet the sheer number of options and nightmarish accounts has left me frozen - unable to make an informed decision as to how to start. I've made a few attempts. dd failed after about 2 hours, as, although the drives appeared to be identical on the surface (ATA Seagate Barracudas, Thai not Chinese), the destination drive is slightly smaller. My most recent attempt involved using a Debian CD to format the new drive and then rsync-ing everything over and editing the new drive's grub and fstab to reflect the changes. No joy here either as I hadn't chosen LVM when partitioning the destination drive and it wouldn't boot. As you can probably tell, I'm out of my depth here and a panic-invoking mixture of caution and frustration has prompted me to sign up here. The server itself, although not strictly a production environment, has a very specific installation of Festival, LAME and ffMpeg and provides the back-end for a Text-to-Speech jQuery plugin that I've built over the last 2 years. I'm also planning to rebuild the whole TTS system on Debian as the existing CentOS system still has PHP4 etc. For now though, I'd really like to just shift everything over to a new drive. As this is my first post, please feel free to lay any house rules on me that I might've overlooked; I've been hovering around StackOverflow for a while now but have only just signed up. Many thanks. Update: Thanks for your responses so far - it's much appreciated and makes me feel a little more confident when I can double-check things here. I had the idea of doing a fresh install of CentOS (from the original disk) on the new drive so the partitions and LVM were all set up correctly (after disconnecting my source drive to prevent painful mistakes). I then booted into rescue mode from the same CD, and, to avoid a conflicting label, changed the /boot partition's label using e2label to /bootnew. I then changed the VolGroup name using lvm vgrename from VolGroup00 to VolGroup001. I could then boot with both drives in. After mounting the new drive (via its VolGroup001 alias) into /newhd, I rsync-ed over everything I could to the new drive, using -avr switches and backslashes. Like mentioned here. I then disconnected my original source drive again, booted from the liveCD again, changed back the boot partition label from /bootnew to /boot using e2label and then renamed the VolGroup back to VolGroup00. I then rebooted and it went through the familiar start-up routine only to not find a host of files in proc, usr, lib, var etc. The boot did complete but there were lots of red 'FAILS'. I could log in with my existing creds, but the network was kaput, I couldn't startX (desktop GUI) and there were also a few (a lot) of error messages pertaining to iptables. Back to square one. I naively thought I'd nailed it. Shall I just buy a bigger hard drive and attempt the dd route? I've read that this can mess with LVM setups and there's the added risk of working on two unmounted drives at once with a low-level tool. Thanks again.

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• Define a varbinary(max) column using sqlalchemy on MS SQL Server

  - by Mark Hall

  Hi, I'm querying an SQL Server database using SQLAlchemy and need to cast a column to varbinary(max). The thing I am struggling with is the "max" part. I can get the cast to work for any actual number (say varbinary(20)), but I cannot find how to get it to work for the "max" size of the varbinary column. Any pointers? Links? Solutions? Regards, Mark

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• Sqlalchemy complex in_ clause

  - by lostlogic

  I'm trying to find a way to cause sqlalchemy to generate sql of the following form: select * from t where (a,b) in ((a1,b1),(a2,b2)); Is this possible? If not, any suggestions on a way to emulate it? Thanks kindly!

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• SQLAlchemy unsupported type error - and table design issues?

  - by Az

  Hi there, back again with some more SQLAlchemy shenanigans. Let me step through this. My table is now set up as so: engine = create_engine('sqlite:///:memory:', echo=False) metadata = MetaData() students_table = Table('studs', metadata, Column('sid', Integer, primary_key=True), Column('name', String), Column('preferences', Integer), Column('allocated_rank', Integer), Column('allocated_project', Integer) ) metadata.create_all(engine) mapper(Student, students_table) Fairly simple, and for the most part I've been enjoying the ability to query almost any bit of information I want provided I avoid the error cases below. The class it is mapped from is: class Student(object): def __init__(self, sid, name): self.sid = sid self.name = name self.preferences = collections.defaultdict(set) self.allocated_project = None self.allocated_rank = 0 def __repr__(self): return str(self) def __str__(self): return "%s %s" %(self.sid, self.name) Explanation: preferences is basically a set of all the projects the student would prefer to be assigned. When the allocation algorithm kicks in, a student's allocated_project emerges from this preference set. Now if I try to do this: for student in students.itervalues(): session.add(student) session.commit() It throws two errors, one for the allocated_project column (seen below) and a similar error for the preferences column: sqlalchemy.exc.InterfaceError: (InterfaceError) Error binding parameter 4 - probably unsupported type. u'INSERT INTO studs (sid, name, allocated_rank, allocated_project) VALUES (?, ?, ?, ?, ?, ?, ?)' [1101, 'Muffett,M.', 1, 888 Human-spider relationships (Supervisor id: 123)] If I go back into my code I find that, when I'm copying the preferences from the given text files, it actually refers to the Project class which is mapped to a dictionary, using the unique project id's (pid) as keys. Thus, as I iterate through each student via their rank and to the preferences set, it adds not a project id, but the reference to the project id from the projects dictionary. students[sid].preferences[int(rank)].add(projects[int(pid)]) Now this is very useful to me since I can find out all I want to about a student's preferred projects without having to run another check to pull up information about the project id. The form you see in the error has the object print information passed as: return "%s %s (Supervisor id: %s)" %(self.proj_id, self.proj_name, self.proj_sup) My questions are: I'm trying to store an object in a database field aren't I? Would the correct way then, be copying the project information (project id, name, etc) into its own table, referenced by the unique project id? That way I can just have the project id field for one of the student tables just be an integer id and when I need more information, just join the tables? So and so forth for other tables? If the above makes sense, then how does one maintain the relationship with a column of information in one table which is a key index on another table? Does this boil down into a database design problem? Are there any other elegant ways of accomplishing this? Apologies if this is a very long-winded question. It's rather crucial for me to solve this, so I've tried to explain as much as I can, whilst attempting to show that I'm trying (key word here sadly) to understand what could be going wrong.

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• SQLAlchemy - select for update example

  - by Mark

  I'm looking for a complete example of using select for update in SQLAlchemy, but haven't found one googling. I need to lock a single row and update a column, the following code doesn't work (blocks forever): s = table.select(table.c.user=="test",for_update=True) u = table.update().where(table.c.user=="test") u.execute(email="foo") Do I need a commit? How do I do that? As far as I know you need to: begin transaction select ... for update update commit

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• SQLAlchemy returns tuple not dictionary

  - by Ivan

  Hi everyone, I've updated SQLAlchemy to 0.6 but it broke everything. I've noticed it returns tuple not a dictionary anymore. Here's a sample query: query = session.query(User.id, User.username, User.email).filter(and_(User.id == id, User.username == username)).limit(1) result = session.execute(query).fetchone() This piece of code used to return a dictionary in 0.5. My question is how can I return a dictionary?

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• SQLAlchemy: a better way for update with declarative?

  - by hadrien

  I am a SQLAlchemy noob. Let's say I have an user table in declarative mode: class User(Base): __tablename__ = 'user' id = Column(u'id', Integer(), primary_key=True) name = Column(u'name', String(50)) When I know user's id without object loaded into session, I update such user like this: ex = update(User.__table__).where(User.id==123).values(name=u"Bob Marley") Session.execute(ex) I dislike using User.__table__, should I stop worrying with that? Is there a better way to do this? Thanx!

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• SQLAlchemy autocommiting?

  - by muckabout

  I have an issue with SQLAlchemy apparently committing. A rough sketch of my code: trans = self.conn.begin() try: assert not self.conn.execute(my_obj.__table__.select(my_obj.id == id)).first() self.conn.execute(my_obj.__table__.insert().values(id=id)) assert not self.conn.execute(my_obj.__table__.select(my_obj.id == id)).first() except: trans.rollback() raise I don't commit, and the second assert always fails! In other words, it seems the data is getting inserted into the database even though the code is within a transaction! Is this assessment accurate?

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• working with django and sqlalchemy but backend mysql

  - by nazmul hasan

  i am working with python django framework but in model part is sqlalchemy and back end data base is mysql how i will configure them???

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• SQLAlchemy introspection

  - by Shaman

  What I am trying to do is to get from SqlAlchemy entity definition all it's Column()'s, determine their types and constraints, to be able to pre-validate, convert data and display custom forms to user. How can I introspect it? Example: class Person(Base): ''' Represents Person ''' __tablename__ = 'person' # Columns id = Column(String(8), primary_key=True, default=uid_gen) title = Column(String(512), nullable=False) birth_date = Column(DateTime, nullable=False) I want to get this id, title, birth date, determine their restrictions (such as title is string and max length is 512 or birth_date is datetime etc) Thank you

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• Batch select with SQLAlchemy

  - by muckabout

  I have a large set of values V, some of which are likely to exist in a table T. I would like to insert into the table those which are not yet inserted. So far I have the code: for value in values: s = self.conn.execute(mytable.__table__.select(mytable.value == value)).first() if not s: to_insert.append(value) I feel like this is running slower than it should. I have a few related questions: Is there a way to construct a select statement such that you provide a list (in this case, 'values') to which sqlalchemy responds with records which match that list? Is this code overly expensive in constructing select objects? Is there a way to construct a single select statement, then parameterize at execution time?

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• strange SqlAlchemy update behaviour

  - by Max

  I'm new to SqlAlchemy and Elixir, so I've started from tutorial and tried to create table, insert a record, and then update it as follows: #'elixir_test.py' from elixir import * metadata.bind = "postgresql://myuser:mypwd@localhost:5432/dbname" metadata.bind.echo = True class Movie(Entity): title = Field(Unicode(30)) year = Field(Integer) description = Field(UnicodeText) def __repr__(self): return '<Movie "%s" (%d)>' % (self.title, self.year) and in another file in the same directory: from elixir_test import * setup_all() #create table create_all() Movie(title=u"Blade Runner", year=1982) #add record session.commit() #get records Movie.query.all() #trying to update record and commit changes, BUT... movie = Movie.query.first() movie.year = 1983 session.commit() #now we have two records in our table, one #with year=1982 and one with year=1983 Movie.query.all() What did I missed?

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• Sqlalchemy+elixir: How query with a ManyToMany relationship?

  - by Hugo

  Hi, I'm using sqlalchemy with Elixir and have some troubles trying to make a query.. I have 2 entities, Customer and CustomerList, with a many to many relationship. customer_lists_customers_table = Table('customer_lists_customers', metadata, Column('id', Integer, primary_key=True), Column('customer_list_id', Integer, ForeignKey("customer_lists.id")), Column('customer_id', Integer, ForeignKey("customers.id"))) class Customer(Entity): [...] customer_lists = ManyToMany('CustomerList', table=customer_lists_customers_table) class CustomerList(Entity): [...] customers = ManyToMany('Customer', table=customer_lists_customers_table) I'm tryng to find CustomerList with some customer: customer = [...] CustomerList.query.filter_by(customers.contains(customer)).all() But I get the error: NameError: global name 'customers' is not defined customers seems to be unrelated to the entity fields, there's an special query form to work with relationships (or ManyToMany relationships)? Thanks

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• Trouble with copying dictionaries and using deepcopy on an SQLAlchemy ORM object

  - by Az

  Hi there, I'm doing a Simulated Annealing algorithm to optimise a given allocation of students and projects. This is language-agnostic pseudocode from Wikipedia: s ? s0; e ? E(s) // Initial state, energy. sbest ? s; ebest ? e // Initial "best" solution k ? 0 // Energy evaluation count. while k < kmax and e > emax // While time left & not good enough: snew ? neighbour(s) // Pick some neighbour. enew ? E(snew) // Compute its energy. if enew < ebest then // Is this a new best? sbest ? snew; ebest ? enew // Save 'new neighbour' to 'best found'. if P(e, enew, temp(k/kmax)) > random() then // Should we move to it? s ? snew; e ? enew // Yes, change state. k ? k + 1 // One more evaluation done return sbest // Return the best solution found. The following is an adaptation of the technique. My supervisor said the idea is fine in theory. First I pick up some allocation (i.e. an entire dictionary of students and their allocated projects, including the ranks for the projects) from entire set of randomised allocations, copy it and pass it to my function. Let's call this allocation aOld (it is a dictionary). aOld has a weight related to it called wOld. The weighting is described below. The function does the following: Let this allocation, aOld be the best_node From all the students, pick a random number of students and stick in a list Strip (DEALLOCATE) them of their projects ++ reflect the changes for projects (allocated parameter is now False) and lecturers (free up slots if one or more of their projects are no longer allocated) Randomise that list Try assigning (REALLOCATE) everyone in that list projects again Calculate the weight (add up ranks, rank 1 = 1, rank 2 = 2... and no project rank = 101) For this new allocation aNew, if the weight wNew is smaller than the allocation weight wOld I picked up at the beginning, then this is the best_node (as defined by the Simulated Annealing algorithm above). Apply the algorithm to aNew and continue. If wOld < wNew, then apply the algorithm to aOld again and continue. The allocations/data-points are expressed as "nodes" such that a node = (weight, allocation_dict, projects_dict, lecturers_dict) Right now, I can only perform this algorithm once, but I'll need to try for a number N (denoted by kmax in the Wikipedia snippet) and make sure I always have with me, the previous node and the best_node. So that I don't modify my original dictionaries (which I might want to reset to), I've done a shallow copy of the dictionaries. From what I've read in the docs, it seems that it only copies the references and since my dictionaries contain objects, changing the copied dictionary ends up changing the objects anyway. So I tried to use copy.deepcopy().These dictionaries refer to objects that have been mapped with SQLA. Questions: I've been given some solutions to the problems faced but due to my über green-ness with using Python, they all sound rather cryptic to me. Deepcopy isn't playing nicely with SQLA. I've been told thatdeepcopy on ORM objects probably has issues that prevent it from working as you'd expect. Apparently I'd be better off "building copy constructors, i.e. def copy(self): return FooBar(....)." Can someone please explain what that means? I checked and found out that deepcopy has issues because SQLAlchemy places extra information on your objects, i.e. an _sa_instance_state attribute, that I wouldn't want in the copy but is necessary for the object to have. I've been told: "There are ways to manually blow away the old _sa_instance_state and put a new one on the object, but the most straightforward is to make a new object with __init__() and set up the attributes that are significant, instead of doing a full deep copy." What exactly does that mean? Do I create a new, unmapped class similar to the old, mapped one? An alternate solution is that I'd have to "implement __deepcopy__() on your objects and ensure that a new _sa_instance_state is set up, there are functions in sqlalchemy.orm.attributes which can help with that." Once again this is beyond me so could someone kindly explain what it means? A more general question: given the above information are there any suggestions on how I can maintain the information/state for the best_node (which must always persist through my while loop) and the previous_node, if my actual objects (referenced by the dictionaries, therefore the nodes) are changing due to the deallocation/reallocation taking place? That is, without using copy?

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• SQLAlchemy introspection of ORM classes/objects

  - by Adam Batkin

  I am looking for a way to introspect SQLAlchemy ORM classes/entities to determine the types and other constraints (like maximum lengths) of an entity's properties. For example, if I have a declarative class: class User(Base): __tablename__ = "USER_TABLE" id = sa.Column(sa.types.Integer, primary_key=True) fullname = sa.Column(sa.types.String(100)) username = sa.Column(sa.types.String(20), nullable=False) password = sa.Column(sa.types.String(20), nullable=False) created_timestamp = sa.Column(sa.types.DateTime, nullable=False) I would want to be able to find out that the 'fullname' field should be a String with a maximum length of 100, and is nullable. And the 'created_timestamp' field is a DateTime and is not nullable.

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• SQLAlchemy declarative syntax with autoload in Pylons

  - by Juliusz Gonera

  I would like to use autoload to use an existings database. I know how to do it without declarative syntax (model/_init_.py): def init_model(engine): """Call me before using any of the tables or classes in the model""" t_events = Table('events', Base.metadata, schema='events', autoload=True, autoload_with=engine) orm.mapper(Event, t_events) Session.configure(bind=engine) class Event(object): pass This works fine, but I would like to use declarative syntax: class Event(Base): __tablename__ = 'events' __table_args__ = {'schema': 'events', 'autoload': True} Unfortunately, this way I get: sqlalchemy.exc.UnboundExecutionError: No engine is bound to this Table's MetaData. Pass an engine to the Table via autoload_with=<someengine>, or associate the MetaData with an engine via metadata.bind=<someengine> The problem here is that I don't know where to get the engine from (to use it in autoload_with) at the stage of importing the model (it's available in init_model()). I tried adding meta.Base.metadata.bind(engine) to environment.py but it doesn't work. Anyone has found some elegant solution?

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• How to discover table properties from SQLAlchemy mapped object

  - by ssaboum

  Hi, My point is i have a class mapped with a table, in my case in a declarative way, and i want to "discover" table properties, columns, names, relations, from this class : engine = create_engine('sqlite:///' + databasePath, echo=True) # setting up root class for declarative declaration Base = declarative_base(bind=engine) class Ship(Base): __tablename__ = 'ships' id = Column(Integer, primary_key=True) name = Column(String(255)) def __init__(self, name): self.name = name def __repr__(self): return "<Ship('%s')>" % (self.name) So now my goal is from the "Ship" class to get the table columns and their properties from another piece of code. I guess i can deal with it using instrumentation but is there any way provided by the SQLAlchemy API ? Thank you.

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• Filter objects within two seconds of one another using SQLAlchemy

  - by Arrieta

  Hello: I have two tables with a column 'date'. One holds (name, date) and the other holds (date, p1, p2). Given a name, I want to use the date in table 1 to query p1 and p2 from table two; the match should happen if date in table one is within two seconds of date in table two. How can you accomplish this using SQLAlchemy? I've tried (unsuccessfully) to use the between operator and with a clause like: td = datetime.timedelta(seconds=2) q = session.query(table1, table2).filter(table1.name=='my_name').\ filter(between(table1.date, table2.date - td, table2.date + td)) Any thoughts?

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• How do I do a semijoin using SQLAlchemy?

  - by Jason Baker

  http://en.wikipedia.org/wiki/Relational_algebra#Semijoin Let's say that I have two tables: A and B. I want to make a query that would work similarly to the following SQL statement using the SQLAlchemy orm: SELECT A.* FROM A, B WHERE A.id = B.id AND B.type = 'some type'; The thing is that I'm trying to separate out A and B's logic into different places. So I'd like to make two queries that I can define in separate places: one where A uses B as a subquery, but only returns rows from A. I'm sure this is fairly easy to do, but an example would be nice if someone could show me.

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• How do you get SQLAlchemy to override MySQL "on update CURRENT_TIMESTAMP"

  - by nocola

  I've inherited an older database that was setup with a "on update CURRENT_TIMESTAMP" put on a field that should only describe an item's creation. With PHP I have been using "timestamp=timestamp" on UPDATE clauses, but in SQLAlchemy I can't seem to force the system to use the set timestamp. Do I have no choice and need to update the MySQL table (millions of rows)? foo = session.query(f).get(int(1)) ts = foo.timestamp setattr(foo, 'timestamp', ts) setattr(foo, 'bar', bar) www_model.www_Session.commit() I have also tried: foo = session.query(f).get(int(1)) setattr(foo, 'timestamp', foo.timestamp) setattr(foo, 'bar', bar) www_model.www_Session.commit()

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• Clear sqlalchemy reflection cache

  - by OrganicPanda

  Hi all, I'm using sqlalchemy's reflection tools to get a Table object. I do this because these tables are dynamic and tables/columns can change. Here's the code I'm using: def getTableByReflection(self, tableName, metadata, engine): return Table(tableName, metadata, autoload = True, autoload_with = engine) The problem is that when the above code is run twice it seems to return the same results regardless of whether or not the columns have changed. I have tried refreshing using the mysession.refresh(mytable) but that fails because the table is not attached to any metadata - which makes sense but then why am I seeing cached results? Is there any way to tell the metadata/engine/session to forget about this table and let me load it cleanly?

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• Many-to-one relationship in SQLAlchemy

  - by Arrieta

  This is a beginner-level question. I have a catalog of mtypes: mtype_id name 1 'mtype1' 2 'mtype2' [etc] and a catalog of Objects, which must have an associated mtype: obj_id mtype_id name 1 1 'obj1' 2 1 'obj2' 3 2 'obj3' [etc] I am trying to do this in SQLAlchemy by creating the following schemas: mtypes_table = Table('mtypes', metadata, Column('mtype_id', Integer, primary_key=True), Column('name', String(50), nullable=False, unique=True), ) objs_table = Table('objects', metadata, Column('obj_id', Integer, primary_key=True), Column('mtype_id', None, ForeignKey('mtypes.mtype_id')), Column('name', String(50), nullable=False, unique=True), ) mapper(MType, mtypes_table) mapper(MyObject, objs_table, properties={'mtype':Relationship(MType, backref='objs', cascade="all, delete-orphan")} ) When I try to add a simple element like: mtype1 = MType('mtype1') obj1 = MyObject('obj1') obj1.mtype=mtype1 session.add(obj1) I get the error: AttributeError: 'NoneType' object has no attribute 'cascade_iterator' Any ideas?

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• SQLAlchemy - loading user by username

  - by keithjgrant

  Just diving into pylons here, and am trying to get my head around the basics of SQLALchemy. I have figured out how to load a record by id: user_q = session.query(model.User) user = user_q.get(user_id) But how do I query by a specific field (i.e. username)? I assume there is a quick way to do it with the model rather than hand-building the query. I think it has something with the add_column() function on the query object, but I can't quite figure out how to use it. I've been trying stuff like this, but obviously it doesn't work: user_q = meta.Session.query(model.User).add_column('username'=user_name) user = user_q.get()

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• Creating tables with pylons and SQLAlchemy

  - by Sid

  I'm using SQLAlchemy and I can create tables that I have defined in /model/__init__.py but I have defined my classes, tables and their mappings in other files found in the /model directory. For example I have a profile class and a profile table which are defined and mapped in /model/profile.py To create the tables I run: paster setup-app development.ini But my problem is that the tables that I have defined in /model/__init__.py are created properly but the table definitions found in /model/profile.py are not created. How can I execute the table definitions found in the /model/profile.py so that all my tables can be created? Thanks for the help!

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• How to improve the speed of a loop containing a sqlalchemy query statement as conditional

  - by LtPinback

  This loop checks if a record is in the sqlite database and builds a list of dictionaries for those records that are missing and then executes a multiple insert statement with the list. This works but it is very slow (at least i think it is slow) as it takes 5 minutes to loop over 3500 queries. I am a complete newbie in python, sqlite and sqlalchemy so I wonder if there is a faster way of doing this. list_dict = [] session = Session() for data in data_list: if session.query(Class_object).filter(Class_object.column_name_01 == data[2]).filter(Class_object.column_name_00 == an_id).count() == 0: list_dict.append({'column_name_00':a_id, 'column_name_01':data[2]}) conn = engine.connect() conn.execute(prices.insert(),list_dict) conn.close() session.close() edit: I moved session = Session() outside the loop. Did not make a difference.

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