Re: HOWTO: Create a ManyToMany Relationship?

[Timothy W. Cook]

Thanks Mike. Yes, the get_or_create works great in my ForeignKey situation
(Paper in a Journal) but I am not so sure it is a good choice here.  For
one thing the incoming data makes it very difficult to filter out Authors.
 There isn't enough real information to tell if it is the same person or
not.  :-(  So, I have to do multiple checks and take a guess.




On Wed, Oct 23, 2013 at 4:33 AM, Mike Dewhirst wrote:

> On 23/10/2013 11:51am, Pepsodent Cola wrote:
>
>> I'm a beginner so I can only answer your first question.  The below link
>> has helped me with 1:M and N:M relationship experiments.
>>
>> Can someone point me to where this is explained in the docs (1.6)?
>>
>>
>> https://docs.djangoproject.**com/en/1.6/topics/db/examples/
>>
>
> https://docs.djangoproject.**com/en/1.6/ref/models/fields/#**
> manytomanyfield
>
> Also, a couple of paragraphs below that ...
>
> https://docs.djangoproject.**com/en/1.6/ref/models/fields/#**
> django.db.models.**ManyToManyField.through
>
> ... where it explains that you can have your own table for the m2m
> relationship if you want to store data about the relationship itself.
>
> For this to make sense you need to declare a model class for that table
> with fields for the extra data. Note that this isn't necessary for ordinary
> m2m relationships because Django does it implicitly.
>
> Anyway, if you make an extra table, it needs a FK to each of the other
> tables. Maybe like ...
>
> class AuthorPaper(models.Model):
> author = models.ForeignKey('Author')
> paper = models.ForeignKey('Paper')
> gossip = models.TextField()
>
> Now this being a model in your own code means you can deal with it in more
> or less the same way as all the other models in your views etc.
>
> I haven't read the code below in any detail so this is probably off the
> mark but there is a get_or_create method which might be useful.
>
> https://docs.djangoproject.**com/en/1.5/ref/models/**
> querysets/#django.db.models.**query.QuerySet.get_or_create
>
> hth
>
> Mike
>
>
>>
>>
>>
>>
>> On Tuesday, October 22, 2013 11:59:14 PM UTC+2, Timothy W. Cook wrote:
>>
>> Can someone point me to where this is explained in the docs (1.6)?
>>
>> I have a ManyToMany relationship in my models between Author and
>> Paper.
>>
>> I am processing an XML file to create records for Papers.
>>
>> I want to check if an Author exists and if not create the record.
>>
>> This was quite easy for Foreign Key relationships.  But I can't get
>> my head around how to do this for ManyToMany.  All of my Authors are
>> created correctly.  But none are automatically selected for the
>> Papers.
>>
>> Some code:
>>
>> class AuthorManager(models.Manager):
>>  def create_author(self, name, email, affl):
>>  a = self.create(name=name, email=email, affiliation=affl)
>>  a.save()
>>  return a
>>
>> class Author(models.Model):
>>  name = models.CharField("Name", max_length=255, db_index=True,
>> null=True, blank=True, help_text="")
>>  email = models.EmailField("Email", max_length=255, null=True,
>> blank=True, help_text="")
>>  affiliation = models.CharField("Affiliation"**, max_length=255,
>> null=True, blank=True, help_text="")
>>
>>  objects = AuthorManager()
>>
>>  def __str__(self):
>>  return self.name 
>>
>>
>>
>> def import_pubmed_xml(obj, f):
>> ...
>>  p =
>> Paper.objects.create_paper(**ptitle,rid,jid,jyear,jvol,**jissue,lang)
>>
>>  #authors
>>  affl = article.xpath("./Affiliation/**text()")
>>  if affl: affl = affl[0]
>>  else: affl = 'unknown'
>>  affl = affl.strip()
>>
>>  authorlist = article.xpath("./AuthorList")
>>  for authorentry in authorlist:
>>  for author in authorentry:
>>  lname = author.xpath("./LastName/text(**)")
>>  if lname:
>>  lname = lname[0]
>>  else:
>>  lname = 'unknown'
>>  fname = author.xpath("./ForeName/text(**)")
>>  if fname:
>>  fname = fname[0]
>>  else:
>>  fname = 'unknown'
>>  initials = author.xpath("./Initials/text(**)")
>>  if initials:
>>  initials = initials[0]
>>  else:
>>  initials = ''
>>
>>  

Re: HOWTO: Create a ManyToMany Relationship?

[Timothy W. Cook]

Thanks for the link.
The add() method was what I was missing.

Changing the one line to p.authors.add(a.id), fixed it.




On Tue, Oct 22, 2013 at 10:51 PM, Pepsodent Cola wrote:

> I'm a beginner so I can only answer your first question.  The below link
> has helped me with 1:M and N:M relationship experiments.
>
> Can someone point me to where this is explained in the docs (1.6)?
>
>
> https://docs.djangoproject.com/en/1.6/topics/db/examples/
>
>
>
>
>
> On Tuesday, October 22, 2013 11:59:14 PM UTC+2, Timothy W. Cook wrote:
>>
>> Can someone point me to where this is explained in the docs (1.6)?
>>
>> I have a ManyToMany relationship in my models between Author and Paper.
>>
>> I am processing an XML file to create records for Papers.
>>
>> I want to check if an Author exists and if not create the record.
>>
>> This was quite easy for Foreign Key relationships.  But I can't get my
>> head around how to do this for ManyToMany.  All of my Authors are created
>> correctly.  But none are automatically selected for the Papers.
>>
>> Some code:
>>
>> class AuthorManager(models.Manager):
>> def create_author(self, name, email, affl):
>> a = self.create(name=name, email=email, affiliation=affl)
>> a.save()
>> return a
>>
>> class Author(models.Model):
>> name = models.CharField("Name", max_length=255, db_index=True,
>> null=True, blank=True, help_text="")
>> email = models.EmailField("Email", max_length=255, null=True,
>> blank=True, help_text="")
>> affiliation = models.CharField("Affiliation"**, max_length=255,
>> null=True, blank=True, help_text="")
>>
>> objects = AuthorManager()
>>
>> def __str__(self):
>> return self.name
>>
>>
>> def import_pubmed_xml(obj, f):
>> ...
>> p = Paper.objects.create_paper(**ptitle,rid,jid,jyear,jvol,**
>> jissue,lang)
>>
>> #authors
>> affl = article.xpath("./Affiliation/**text()")
>> if affl: affl = affl[0]
>> else: affl = 'unknown'
>> affl = affl.strip()
>>
>> authorlist = article.xpath("./AuthorList")
>> for authorentry in authorlist:
>> for author in authorentry:
>> lname = author.xpath("./LastName/text(**)")
>> if lname:
>> lname = lname[0]
>> else:
>> lname = 'unknown'
>> fname = author.xpath("./ForeName/text(**)")
>> if fname:
>> fname = fname[0]
>> else:
>> fname = 'unknown'
>> initials = author.xpath("./Initials/text(**)")
>> if initials:
>> initials = initials[0]
>> else:
>> initials = ''
>>
>> a_name = (lname +', '+fname + ' ' +initials).strip()
>> print(a_name)
>> email = ''
>> #need to lookup Author by name then check affiliation. If
>> not found then create it.
>> try:
>> a = Author.objects.get(name=a_**name)
>> p.authors.id = a.id
>> p.save()
>> except ObjectDoesNotExist:
>> a = Author.objects.create_author(**a_name, email,
>> affl)
>> p.authors.id = a.id
>> p.save()
>> ==**=
>>
>> Thanks in Advance,
>> Tim
>>
>>
>>
>>
>>
>> --
>> MLHIM VIP Signup: http://goo.gl/22B0U
>> ==**==
>> Timothy Cook, MSc   +55 21 94711995
>> MLHIM http://www.mlhim.org
>> Like Us on FB: 
>> https://www.facebook.com/**mlhim2
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>> LinkedIn 
>> Profile:http://www.linkedin.**com/in/timothywaynecook
>>
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Re: HOWTO: Create a ManyToMany Relationship?

[Mike Dewhirst]

On 23/10/2013 11:51am, Pepsodent Cola wrote:

I'm a beginner so I can only answer your first question.  The below link
has helped me with 1:M and N:M relationship experiments.

Can someone point me to where this is explained in the docs (1.6)?


https://docs.djangoproject.com/en/1.6/topics/db/examples/


https://docs.djangoproject.com/en/1.6/ref/models/fields/#manytomanyfield

Also, a couple of paragraphs below that ...

https://docs.djangoproject.com/en/1.6/ref/models/fields/#django.db.models.ManyToManyField.through

... where it explains that you can have your own table for the m2m 
relationship if you want to store data about the relationship itself.


For this to make sense you need to declare a model class for that table 
with fields for the extra data. Note that this isn't necessary for 
ordinary m2m relationships because Django does it implicitly.


Anyway, if you make an extra table, it needs a FK to each of the other 
tables. Maybe like ...


class AuthorPaper(models.Model):
author = models.ForeignKey('Author')
paper = models.ForeignKey('Paper')
gossip = models.TextField()

Now this being a model in your own code means you can deal with it in 
more or less the same way as all the other models in your views etc.


I haven't read the code below in any detail so this is probably off the 
mark but there is a get_or_create method which might be useful.


https://docs.djangoproject.com/en/1.5/ref/models/querysets/#django.db.models.query.QuerySet.get_or_create

hth

Mike







On Tuesday, October 22, 2013 11:59:14 PM UTC+2, Timothy W. Cook wrote:

Can someone point me to where this is explained in the docs (1.6)?

I have a ManyToMany relationship in my models between Author and Paper.

I am processing an XML file to create records for Papers.

I want to check if an Author exists and if not create the record.

This was quite easy for Foreign Key relationships.  But I can't get
my head around how to do this for ManyToMany.  All of my Authors are
created correctly.  But none are automatically selected for the Papers.

Some code:

class AuthorManager(models.Manager):
 def create_author(self, name, email, affl):
 a = self.create(name=name, email=email, affiliation=affl)
 a.save()
 return a

class Author(models.Model):
 name = models.CharField("Name", max_length=255, db_index=True,
null=True, blank=True, help_text="")
 email = models.EmailField("Email", max_length=255, null=True,
blank=True, help_text="")
 affiliation = models.CharField("Affiliation", max_length=255,
null=True, blank=True, help_text="")

 objects = AuthorManager()

 def __str__(self):
 return self.name 


def import_pubmed_xml(obj, f):
...
 p =
Paper.objects.create_paper(ptitle,rid,jid,jyear,jvol,jissue,lang)

 #authors
 affl = article.xpath("./Affiliation/text()")
 if affl: affl = affl[0]
 else: affl = 'unknown'
 affl = affl.strip()

 authorlist = article.xpath("./AuthorList")
 for authorentry in authorlist:
 for author in authorentry:
 lname = author.xpath("./LastName/text()")
 if lname:
 lname = lname[0]
 else:
 lname = 'unknown'
 fname = author.xpath("./ForeName/text()")
 if fname:
 fname = fname[0]
 else:
 fname = 'unknown'
 initials = author.xpath("./Initials/text()")
 if initials:
 initials = initials[0]
 else:
 initials = ''

 a_name = (lname +', '+fname + ' ' +initials).strip()
 print(a_name)
 email = ''
 #need to lookup Author by name then check
affiliation. If not found then create it.
 try:
 a = Author.objects.get(name=a_name)
p.authors.id  = a.id 
 p.save()
 except ObjectDoesNotExist:
 a = Author.objects.create_author(a_name, email,
affl)
p.authors.id  = a.id 
 p.save()
===

Thanks in Advance,
Tim





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Re: HOWTO: Create a ManyToMany Relationship?

[Pepsodent Cola]

I'm a beginner so I can only answer your first question.  The below link 
has helped me with 1:M and N:M relationship experiments.

Can someone point me to where this is explained in the docs (1.6)?


https://docs.djangoproject.com/en/1.6/topics/db/examples/





On Tuesday, October 22, 2013 11:59:14 PM UTC+2, Timothy W. Cook wrote:
>
> Can someone point me to where this is explained in the docs (1.6)?
>
> I have a ManyToMany relationship in my models between Author and Paper.  
>
> I am processing an XML file to create records for Papers.
>
> I want to check if an Author exists and if not create the record. 
>
> This was quite easy for Foreign Key relationships.  But I can't get my 
> head around how to do this for ManyToMany.  All of my Authors are created 
> correctly.  But none are automatically selected for the Papers. 
>
> Some code:
>
> class AuthorManager(models.Manager):
> def create_author(self, name, email, affl):
> a = self.create(name=name, email=email, affiliation=affl)
> a.save()
> return a
>
> class Author(models.Model):
> name = models.CharField("Name", max_length=255, db_index=True, 
> null=True, blank=True, help_text="")
> email = models.EmailField("Email", max_length=255, null=True, 
> blank=True, help_text="")
> affiliation = models.CharField("Affiliation", max_length=255, 
> null=True, blank=True, help_text="")
>
> objects = AuthorManager()
>
> def __str__(self):
> return self.name
>
>
> def import_pubmed_xml(obj, f):
> ...
> p = 
> Paper.objects.create_paper(ptitle,rid,jid,jyear,jvol,jissue,lang)
>
> #authors
> affl = article.xpath("./Affiliation/text()")
> if affl: affl = affl[0]
> else: affl = 'unknown'
> affl = affl.strip()
>
> authorlist = article.xpath("./AuthorList")
> for authorentry in authorlist:
> for author in authorentry:
> lname = author.xpath("./LastName/text()")
> if lname:
> lname = lname[0]
> else:
> lname = 'unknown'
> fname = author.xpath("./ForeName/text()")
> if fname:
> fname = fname[0]
> else:
> fname = 'unknown'
> initials = author.xpath("./Initials/text()")
> if initials:
> initials = initials[0]
> else:
> initials = ''
>
> a_name = (lname +', '+fname + ' ' +initials).strip()
> print(a_name)
> email = ''
> #need to lookup Author by name then check affiliation. If 
> not found then create it.
> try:
> a = Author.objects.get(name=a_name)
> p.authors.id = a.id
> p.save()
> except ObjectDoesNotExist:
> a = Author.objects.create_author(a_name, email, affl)
> p.authors.id = a.id
> p.save()
> ===
>
> Thanks in Advance,
> Tim
>
>
>
>
>
> -- 
> MLHIM VIP Signup: http://goo.gl/22B0U
> 
> Timothy Cook, MSc   +55 21 94711995
> MLHIM http://www.mlhim.org
> Like Us on FB: https://www.facebook.com/mlhim2
> Circle us on G+: http://goo.gl/44EV5
> Google Scholar: http://goo.gl/MMZ1o
> LinkedIn Profile:http://www.linkedin.com/in/timothywaynecook
>  

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