I've got a question which I'll ask two ways: short & generic, so future generations of StackOverflow readers will benefit, and Long & Detailed, so I can get my work done without screwing anything up.
Short & Generic Version:
How do I make Django generate a table-like form where some info in the table is from the database, and the user fills in the rest? On form submission, each row in the table should become a record in the database (after it's validated, of course).
What's the cleanest way to do this? What's this mode of interaction cannonically called?
Example Form
|=============================================================|
| QueriedValue | CalculatedValue | User_data | More_User_data |
|_____________________________________________________________|
| Foo 1 | Bar 1 | | |
| Foo 2 | Bar 2 | | |
| Foo 3 | Bar 3 | | |
... ... ... ... |
| Foo n | Bar n | | |
|=============================================================|
++++++++++
| Submit |
++++++++++
Resulting Database Records
TimeStamp + fk_Foo = natural primary key for this table
________________
/ \
|===========================================================|
| TimeStamp | fk_Foo | User_data | More_User_data |
|___________________________________________________________|
| submit_time | Foo 1 | Datum 1 | AnotherDatum 1 |
| submit_time | Foo 2 | Datum 2 | AnotherDatum 2 |
| submit_time | Foo 3 | Datum 3 | AnotherDatum 3 |
|... ... ... ... |
| submit_time | Foo n | Datum n | AnotherDatum n |
|===========================================================|
Long Version
I'm writing a web app to track gas cylinder usage at my company. We have a bunch of gas plumbing in our building, and we need to know which gas cylinder was hooked up to which gas line at what time.
I'd like two forms for the technicians to fill out:
Daily Inventory: Every morning, the stockroom guy needs to look at each gas line and record the line's pressure, and the reference number of the bottle. This generates bunch of 4-tuple records (time, line, bottle, psi); one for each line, every morning.
As-Needed Bottle Change: After doing the daily inventory, if a bottle is almost out it needs to be changed, and that change needs to be logged. This should add another entry to the table of bottles for the new bottle, and another 4-tuple with the new (time, line, bottle, psi) info for the new connection. This happens to a random line a few times a week, but not every day.
So to keep track of this I'm writing a Django application. I've got the following models:
# models.py
class GasFarm(models.Model):
"""
Represents a gas farm -- a collection of lines that are grouped together and managed as a unit.
"""
name = models.CharField(max_length=30, unique=True)
def __unicode__(self):
return self.name
class Bottle(models.Model):
"""
Represents a gas bottle -- the physical cylinder -- that contains a mixture of gases.
"""
# Options
get_latest_by = 'date_added'
# Fields
BACKGROUND_TYPES = (
('h2/n2', "H2/N2"),
('h2/air', "H2/Air"),
('h2', "H2"),
('n2', "N2"),
('other', "Other"),
)
ppm = models.FloatField()
mix = models.CharField(max_length=50, choices=BACKGROUND_TYPES, default='n2')
ref = models.CharField(max_length=50, unique=True) # Every bottle has a unique ref or somebody fucked up.
cert_date = models.DateTimeField()
date_added = models.DateTimeField(default=timezone.now())
def pct(self):
return float(self.ppm)/10**4
def __unicode__(self):
return "{} ({}% {})".format(self.ref, self.pct(), self.mix,)
class Line(models.Model):
"""
Represents a gas line -- the physical plumbing -- that delivers gas from the bottles to the test stations.
It is assumed that a gas line can have zero or one gas bottles attached to it at any given time. The Line model
maps bottle objects and time-sensitive Reading objects to test stations.
"""
# Fields
gasfarm = models.ForeignKey(GasFarm)
number = models.CharField(max_length=10, unique=True)
bottles = models.ManyToManyField(Bottle, through='Reading')
# Calculated fields. "current" is definitely not optional -- that's a super common query. The others? I'm not so
# sure...
def current(self):
"""
Returns the most recently recorded Reading object associated with the line
"""
return self.reading_set.latest(field_name='time')
current.short_description = "latest reading"
def last_checked(self):
"""
Returns the date & time at which the most recent Reading object associated with this line was logged
"""
return self.current().time
last_checked.short_description = "last updated"
def has_recent_reading(self):
"""
Boolean flag for whether the reading is probably valid, or if someone needs to go out and take a new one.
"""
latest_reading = self.current().time
return timezone.now() - latest_reading < datetime.timedelta(days=3)
has_recent_reading.boolean = True
has_recent_reading.short_description = "Is data current?"
def __unicode__(self):
return self.number
class Reading(models.Model):
"""
A Reading links a Bottle to a Line at a given time, and provides a snapshot of the pressure at that time.
"""
# Options
get_latest_by = 'time'
# Fields
line = models.ForeignKey(Line)
bottle = models.ForeignKey(Bottle)
time = models.DateTimeField()
psi = models.IntegerField(validators=[MaxValueValidator(2500)])
def ref(self):
"""
The reference number of the bottle listed in the reading
"""
return self.bottle.ref
def ppm(self):
"""
The PPM concentration of the bottle listed in the reading
"""
return self.bottle.ppm
def pct(self):
"""
The % concentration of the bottle listed in the reading
"""
return self.bottle.pct()
def mix(self):
"""
The gas mix (e.g. H2/N2) of the associated bottle
"""
return self.bottle.mix
def __unicode__(self):
# Example:
# A0: 327.3 PPM H2/N2 2300 psi
return "{}, {}: {} PPM {} {} psi".format(self.line, self.time, self.ppm(), self.mix(), self.psi)
I've populated the database with our back-log of data using some scripts, and I've written a few views to pull data out of the databse; I'm happy with them so far, and the results look very promising -- at least for displaying stored data.
But I'm not sure how to cleanly populate the database using HTML forms. I'd like the forms to be basically two separate "worksheets" -- like the kind the DMV gives you, with nice clear instructions #justkidding.
Form 1: Daily Inventory
The form would list all the lines in a given farm, display what bottle should be on each line (based on previous readings/updates), and then prompt the user to enter a value. This would require that the technician update the pressure of every bottle on every line each time they submit the form -- we want a global snapshot of the whole gas system. In a perfect world, the form would pre-fill the current time and each line's most recent pressure reading into the Reading Time and Pressure fields to ease data entry.
# Cells with brackets [] are system-supplied, non-editable data displayed in the table.
# Cells without brackets are pre-filled with sensible defaults, but are user editable.
| [Line] | [Current Bottle] | Reading Time | Pressure (psi) |
===============================================================
| [A0] | [15-1478334] | 2014-7-14 9:34 | 2400 |
| [A1] | [15-1458661] | 2014-7-14 9:34 | 500 |
| [A2] | [15-4851148] | 2014-7-14 9:34 | 1850 |
| [A3] | [15-1365195] | 2014-7-14 9:34 | 700 |
...
...
| [C18] | [15-9555813] | 2014-7-14 9:34 | 2350 |
|=====================================================================|
After reading through the Django docs on Forms, ModelForms, and Formsets, I've written some code that does almost everything I want -- but the Line and Bottle information are editable form fields, and I need them to be static guideposts for filling in the rest of the form. They do need to be present in the generated database records, though.
I am dimly aware of the readonly and disabled attributes, and of what appear to be kludgy solutions to clean data from the POST variable in the response when you want to have read-only stuff in forms, but I'm still not clear on how those work or why they're necessary. I'm wondering if there's a cleaner way to get what I"m after? Perhaps forms with programmatically generated headings, or annotations? That's all I really want: an auto-generated guide to filling out the form.
# Forms.py
class PressureReadingUpdate(forms.ModelForm):
class Meta:
model = models.Reading
PsiReadingFormset = formset_factory(PressureReadingUpdate, extra=0)
# views.py
def update_pressure(request):
if request.method == 'POST':
formset = forms.PsiReadingFormset(request.POST)
if formset.is_valid():
cd = formset.cleaned_data
# do something? I'm not here yet...
else:
lines = models.Line.objects.all()
now = datetime.datetime.now()
initial = [{'line': l,
'psi': l.current().psi,
"bottle": l.current().bottle,
'time': now} for l in lines]
formset = forms.PsiReadingFormset(initial=initial,)
return render(request, 'gas_tracking/gasfarm_form_psi_reading.html', {'formset': formset})
Form 2: Change a Gas Bottle
I'd like a list of all the gas lines, with the current bottle & pressure (easy-- this is done elsewhere), and then a button that makes a pop-up window where you can submit a new bottle, much like you find in the admin interface. How do I make pop-up windows? How do I make buttons? I'm not even sure where to start with this one yet
I'm still very new to Django, and I've searched high and low, but haven't found anything that answers my question -- maybe I'm just not using the right keywords?
Thanks for your help.
-Matt
Dynamically generating Forms using FormSets
So I figured this out (after much googling and swearing and gnashing of teeth). Malcolm Tredinnick made a blog post about exactly what I wanted to do, which a kind soul preserved on Django Snippets
Using Malcom's code as a model, I solved my problem and it works like a charm
class PressureReadingUpdate(forms.Form):
"""
Form that asks for the pressure of a line given some attributes of that line.
"""
psi = forms.IntegerField(widget=forms.NumberInput)
def __init__(self, *args, **kwargs):
self.line = kwargs.pop('line')
kwargs['auto_id'] = "%s".format(self.line.number)
super(PressureReadingUpdate, self).__init__(*args, **kwargs)
class BasePsiReadingFormset(BaseFormSet):
"""
Formset that constructs a group of PressureReadingUpdate forms by taking a queryset
of Line objects and passing each one in turn to a PressureReadingUpdate form as it
gets constructed
"""
def __init__(self, *args, **kwargs):
self.lines = kwargs.pop('lines')
super(BasePsiReadingFormset, self).__init__(*args, **kwargs)
self.extra = len(self.lines)
self.max_num = len(self.lines)
def _construct_form(self, i, **kwargs):
kwargs['line'] = self.lines[i]
form = super(BasePsiReadingFormset, self)._construct_form(i, **kwargs)
return form
PsiReadingFormset = formset_factory(form=PressureReadingUpdate, formset=BasePsiReadingFormset)
This gives you a Formset with an extra kwarg you can pass down the chain of constructors. You can use it in a view (along with a more typical initial= kwarg) with:
formset = PsiReadingFormset(lines=lines,
initial=[{'psi': l.current().psi} for l in lines],
So here's the best explanation I can think of:
Any kwargs passed to a FormSet like (which gets made by the formset_factory function using a non-default 'BaseFormSet' as a blueprint) get passed along -- mostly unaltered -- to the __init__ method of whatever BaseFormSet the FormSet is based on.
This means you can define custom behavior in BaseFormSet.__init__, and you can relay runtime data to the BaseFormSet.__init__ method by passing it as a keyword argument to FormSet (that's the lines= kwarg in my example above). I use it to set an attribute on on formset (an instance of a FormSet based on 'BasePsiReadingFormset').
Confused yet? I was too at first.
But the real magic is understanding how _construct_forms works: A FormSet calls this function each time it wants to make a new Form in the set. It will relay any unrecognized kwargs to to the constructor of the Form it is supposed to manage a set of.
So you just need to overload your custom BaseFormSet's ._construct_forms to wrap the original _construct_forms of the superclass and inject a new kwarg. This kwarg will then be passed through to the constructor of your custom Form class, and shape the new Form instance according to the Form's initialization function.
And that, ladies and gentlemen, is how you can have a FormSet that has a bunch of similarly-defined but dynamically-generated-and-slightly different forms in it.
After understanding this, I can see the elegance of it. However, it uses some intermediate-to-advanced python, and is neither immediately obvious nor well documented. If you are struggling with this like I did, feel free to message me.
Related
I am implementing search in my project what I want is to concat to column in where clause to get results from table.
Here is what I am doing:
from django.db.models import Q
if 'search[value]' in request.POST and len(request.POST['search[value]']) >= 3:
search_value = request.POST['search[value]'].strip()
q.extend([
Q(id__icontains=request.POST['search[value]']) |
(Q(created_by__first_name=request.POST['search[value]']) & Q(created_for=None)) |
Q(created_for__first_name=request.POST['search[value]']) |
(Q(created_by__last_name=request.POST['search[value]']) & Q(created_for=None)) |
Q(created_for__last_name=request.POST['search[value]']) |
(Q(created_by__email__icontains=search_value) & Q(created_for=None)) |
Q(created_for__email__icontains=search_value) |
Q(ticket_category=request.POST['search[value]']) |
Q(status__icontains=request.POST['search[value]']) |
Q(issue_type__icontains=request.POST['search[value]']) |
Q(title__icontains=request.POST['search[value]']) |
Q(assigned_to__first_name__icontains=request.POST['search[value]']) |
])
Now I want to add another OR condition like:
CONCAT(' ', created_by__first_name, created_by__last_name) like '%'search_value'%'
But when I add this condition to the queryset it becomes AND
where = ["CONCAT_WS(' ', profiles_userprofile.first_name, profiles_userprofile.last_name) like '"+request.POST['search[value]']+"' "]
tickets = Ticket.objects.get_active(u, page_type).filter(*q).extra(where=where).exclude(*exq).order_by(*order_dash)[cur:cur_length]
How do I convert this into an OR condition?
Advanced filters can be solved by
Q() object and
Query expressions like Func(), Value() and F().
The only used trick is a
Custom Lookup "rhs_only" that uses the right-hand-side of the lookup and ignores the left side, because it is easier to use all concatenated fields directly on the right side. A memorable function concat_like encapsulates that all to be easily used in queries.
from django.db.models import F, Func, Lookup, Q, Value
from django.db.models.fields import Field
def concat_like(columns, pattern):
"""Lookup filter: CONCAT_WS(' ', column_0, column_1...) LIKE pattern"""
lhs = '%s__rhs_only' % columns[0]
expr = Func(*(F(x) for x in columns), template="CONCAT_WS(' ', %(expressions)s)")
return Q(**{lhs: Like(expr, Value(pattern))})
class Like(Func):
def as_sql(self, compiler, connection):
arg_sql, arg_params = zip(*[compiler.compile(x) for x in self.source_expressions])
return ("%s LIKE '%s'" % tuple(arg_sql)), arg_params[0] + arg_params[1]
#Field.register_lookup
class RhsOnly(Lookup):
"""Skip the LHS and evaluate the boolean RHS only"""
lookup_name = 'rhs_only'
def as_sql(self, compiler, connection):
return self.process_rhs(compiler, connection)
All boolean expression and related objects are supported by this code. All arguments are correctly escaped.
Example usage:
>>> qs = MyModel.objects.filter(Q(id=1) | concat_like(('first_name', 'surname'), 'searched'))
>>> str(qs.query) # sql output simplified here
"SELECT .. WHERE id=1 OR (CONCAT_WS(' ', first_name, surname) LIKE 'searched')"
Relevant documentation:
https://docs.djangoproject.com/en/1.11/ref/models/expressions/#func-expressions
See also... Value() and F()
https://docs.djangoproject.com/en/1.11/topics/db/aggregation/#aggregations-and-other-queryset-clauses
You can reference annotated fields from inside the filter method. As such, you can filter against two concatenated fields and add it as another OR condition like this:
from django.db.models import F, Func, Value
# Because we added user_full_name as an annotation below,
# we can refer to it in the filters
q.extend([
Q(id__icontains=request.POST['search[value]']) |
(Q(created_by__first_name=request.POST['search[value]']) & Q(created_for=None)) |
Q(created_for__first_name=request.POST['search[value]']) |
(Q(created_by__last_name=request.POST['search[value]']) & Q(created_for=None)) |
Q(created_for__last_name=request.POST['search[value]']) |
(Q(created_by__email__icontains=search_value) & Q(created_for=None)) |
Q(created_for__email__icontains=search_value) |
Q(ticket_category=request.POST['search[value]']) |
Q(status__icontains=request.POST['search[value]']) |
Q(issue_type__icontains=request.POST['search[value]']) |
Q(title__icontains=request.POST['search[value]']) |
Q(assigned_to__first_name__icontains=request.POST['search[value]']) |
Q(user_full_name__icontains=request.POST['search[value]']) # <------
])
# Add the annotation to your queryset
# I'm not actually sure what the related_name or field_name for your user
# profiles are, so I'm pretending that tickets have a profile foreignkey field
# to where the first_name and last_name fields are
user_full_name_expr = Func(Value(' '), F('profile__first_name'), F('profile__last_name'), function='CONCAT_WS')
# The next two lines can be combined as long as the annotation comes first.
tickets = Ticket.objects.annotate(user_full_name=user_full_name_expr)
tickets = tickets.get_active(u, page_type).filter(*q).exclude(*exq).order_by(*order_dash)[cur:cur_length]
For fun, here's a working example based on the User model.
from django.contrib.auth.models import User
from django.db.models import F, Func, Value
User.objects.create(username='john', first_name='John', last_name='Jingleheimer-Schmidt')
User.objects.create(username='mike', first_name='Michael', last_name='Finnigan')
foo = User.objects.annotate(full_name=Func(Value(' '), F('first_name'), F('last_name'), function='CONCAT_WS'))
print(foo.filter(full_name__icontains='john'))
# outputs: [<User: john>]
What you need is, for create search FullText. I recommend use (http://haystacksearch.org/)
See documentation of Django (https://docs.djangoproject.com/en/1.11/ref/contrib/postgres/search/)
I am trying to create a simple charting web app using pygal and flask to chart some financial data I have stored in a mysql database. The data in the DB is hierarchical, and I want the app to start at the top of the hierarchy and allow the user to drill down by simply clicking on the relevant parts of the chart.
I am using flask to display the dynamically generated pygal charts.
Sample DB data:
guid | name | value | parentGuid | Description
------------------------------------------------
1234 | cat1 | 1 | null | Blah, blah
4567 | cat2 | 55 | null | asfdsa
8901 | cat3 | 22 | 1234 | asfdsa
5435 | cat4 | 3 | 8901 | afdsa
etc...
I have no problem drilling down the hierarchy using python + sql, but where I'm stumped is how I drill down using links in my pygal chart.
#app.route('/', methods=['GET', 'POST'])
def index():
if request.method == 'POST':
chart = graph_sub(request.form['guid'])
return render_template('Graph3.html', chart=chart)
else:
chart = graph_main()
return render_template('Graph3.html', chart=chart)
def graph_main():
""" render svg graph """
line_chart = pygal.HorizontalBar()
line_chart.title = 'Root Accounts'
RootAccts = GetRootAccounts() # Returns a list of lists containing accounts and account data.
for Acct in RootAccts:
line_chart.add({
'title': Acct[1], # Acct Name
'tooltip': Acct[4], # Acct description
'xlink': {'href': '/'} # Hyperlink that I want to pass POST data back to the form.
}, [{
'value': Acct[2]), # Acct Value
'label': Acct[4], # Acct Description
'xlink': {'href': '/'} # Hyperlink that I want to pass POST data back to the form.
}])
return line_chart.render()
def graph_sub(parentGuid):
### This works fine if I pass a parent GUID to it
### Now the question is how do I pass the guid to it from my pygal chart?
return line_chart.render()
So when I click on the links embedded in the pygal chart
'xlink': {'href': '/'}
How can I make it redirect back to the same page and pass the GUID of the selected account as POST data? Or is there another way to do this that doesn't involve POST?
The page reloading every time they click something so I'm hoping to keep this as simple as possible without having to involve ajax/java/etc... though if there are no other options I am open to it.
I don't have it coded yet, but there will also be some additional form controls added to the page that will allow the user to set date ranges to control how much data is displayed. I was planning to use POST to pass user input around, but before I get too far down that road, I need to figure out how I can manage this base functionality.
Thoughts?
I have a Django view that uses one form multiple times. The form is saving relationship Subgroup id as a foreign key and Student id as a foreign key .
The problem I'm having is when I try to save information to database it only saves the last record.
For example (database model):
1 858 | Pump | Iron
2 78 | Madagaskar| Thomas
And if Im trying to split them into seperate groups, only Madagaskar his data is saved:
id | timestamp | student_Id_id | subgroup_Id_id |
+----+----------------------------+---------------+----------------+
| 62 | 2016-05-06 10:54:49.022000 | 2 | 91 |
The form looks like this:
class ApplicationFormaFull1(MultiModelForm):
form_classes = {
'sub1': FormSubgroup,
'sub2': FormSubgroup,
'stud_sub': FormStudent_in_Subgroup
}
and my view :
sub = form['sub1'].save(commit=False)
sub.student_group = StudentGroup.objects.get(id=element)
sub.number = 1
sub.type = 'Other'
sub.student_count = firstSubgroup
sub.save()
sub1 = form['sub2'].save(commit=False)
sub1.student_group = StudentGroup.objects.get(id=element)
sub1.number = 2
sub1.type = 'Others'
sub1.student_count = secondSubgroup
sub1.save()
if (counter%2==1):
stud_sub = form['stud_sub'].save(commit=True)
stud_sub.subgroup_Id = sub
stud_sub.student_Id = Student.objects.get(id=student)
stud_sub.save()
else:
stud_sub = form['stud_sub'].save(commit=True)
stud_sub.subgroup_Id = sub1
stud_sub.student_Id = Student.objects.get(id=student)
stud_sub.save()
So to sum up, I want that every form would save its information multiple times (dynamically)
Maybe the solution is that I should store information in the list and after all forms are added, save them one by one ?
stud_sub = form['stud_sub'].save(commit=False)
stud_sub.subgroup_Id = sub
stud_sub.student_Id = Student.objects.get(id=student)
list.add(stud_sub)
...
for i in list:
i.save()
Other solution use formset:
ArticleFormSet = formset_factory(ArticleForm, extra=2)
formset = ArticleFormSet(initial=[
{'title': 'Django is now open source',
'pub_date': datetime.date.today(),}
])
However i dont know how to change title, pub_date and to add everyting to formset dynimically.
Django Code & Reference to Django Bug Report
Given three models as follows (simplified excessively for demonstration...not actually identical related models)
class derp(models.Model):
...
class derp_related_1(models.Model):
fk = models.ForeignKey(derp)
amount = models.DecimalField(max_digits=15, decimal_places=2)
class derp_related_2(models.Model):
fk = models.ForeignKey(derp)
amount = models.DecimalField(max_digits=15, decimal_places=2)
And overriding a queryset in the model admin as follows. (It isn't working because of this django bug.)
class DerpAdmin(admin.ModelAdmin):
...
list_display = ['derp_r1_sum', 'derp_r2_sum']
...
def queryset(self, request):
qs = super(DerpAdmin, self).queryset(request)
qs = qs.annotate(derp_r1_sum=models.Sum('derp_r1__amount', distinct=True))
qs = qs.annotate(derp_r2_sum=models.Sum('derp_r2__amount', distinct=True))
def derp_r1_sum(self, obj):
return u'%s' % obj.derp_r1_sum
def derp_r2_sum(self, obj):
return u'%s' % obj.derp_r2_sum
Example of Unexpected Database Result
Running annotations individually would render something like (with grouping & sums removed)
+---------+--------+
| derp.id | r1_sum |
+---------+--------+
| 2 | 500.00 |
| 2 | 100.00 |
+---------+--------+
r1_sum would be 600.00
and
+---------+--------+
| derp.id | r1_sum |
+---------+--------+
| 2 | 100.00 |
| 2 | 250.00 |
+---------+--------+
r2_sum would be 350.00
If you take qs.query with both annotations included and remove the sums and the grouping it is obvious what the problem is. In this case we're counting everything twice. Get more relations and we have an increasingly ugly increase in both sum columns.
+---------+--------+--------+
| derp.id | r1_sum | r2_sum |
+---------+--------+--------+
| 2 | 500.00 | 100.00 |
| 2 | 500.00 | 250.00 |
| 2 | 100.00 | 100.00 |
| 2 | 100.00 | 250.00 |
+---------+--------+--------+
r1_sum would incorrectly be 1200.00
r2_sum would incorrectly be 700.00
Question, is there a route other than custom SQL?
I can write the query myself easy enough, but if anyone has a suggestion which would avoid the writing of custom SQL that would be awesome.
Thanks for the help.
Edit: Here is a link to the annotations section of the Django documentation. One commenter mentioned the distinct option. This does not work, and I believe it is what is warned about at the bottom of the annotation section in the django documentation on annotation.
Edit2: The raw SQL idea likely is more difficult than I thought as derp.objects.raw('sql here') does not return the queryset object necessary for the admin to use it. Is there a way to use two queries (the real queryset plus a custom one doing the sums) and populate the listview from both? One suggestion I found (which I cannot find again now :S) suggested creating a view that maps to a Model definition which is then set to unmanaged by django (for syncdb). I could then write my custom code, and reference it for inclusion in the original query. This sounds messy. Thoughts?
If you want to stay within Django's queryset, I would consider creating a model superclass that shares the related and common fields and sub-classing for further distinctions. Otherwise, you need to either write custom SQL or get out of the database ORM entirely and manipulate your data in python with Queryset.values or Queryset.values_list
The best way I found to return the correct results was by using queryset.extra().
derp_r1_sum_select = """
select sum(`derp_related_1`.`amount`)
from `derp_related_1`
where `derp_related_1`.`fk` = `derp`.`pk`
"""
derp_r2_sum_select = """
select sum(`derp_related_2`.`amount`)
from `derp_related_2`
where `derp_related_2`.`fk` = `derp`.`pk`"
"""
def queryset(self, request):
qs = super(DerpAdmin, self).queryset(request)
qs = qs.extra(select={'derp_r1_sum': derp_r1_sum_select,
'derp_r2_sum': derp_r2_sum_select})
return qs
I have two Python classes Note and Link mapping to PostgresQL tables. Note has a foreign-key reference to Link, while Link points back to the node through a piece of JSON text. Links point to other things besides Notes but that doesn't matter here.
Note
+------+------------------+---------+
| ID | NAME | NOTE_ID |
+------+------------------+---------+
| 1 | Alice | 5 |
| 2 | Bob | 20 |
| 3 | Carla | 6 |
+------+------------------+---------+
Link
+------+--------------+
| ID | CONTENT |
+------+--------------+
| ... | ... |
| 5 | {"t":1} |
| 6 | {"t":3} |
| ... | ... |
| 20 | {"t":2} |
+------+--------------+
Now what I would like is that whenever I create a new Note
note = Note('Danielle')
it would automatically enter the row
(4, 'Danielle', 21)
into Note, AND enter
(21, '{"t":4}')
into Link. Here's what I have tried so far: I create the Note object and THEN try to create the Link in the #events.after_insert event:
class Note(Entity):
name = Field(Unicode)
link = ManyToOne('Link')
. . .
#events.after_insert
def create_link(self):
"""
Create and persist the short link for this note. Must be done
in this after_insert event because the link table has a foreign
key that points back to the note. We need the note to be
already inserted so we can use its id.
"""
self.link = Link.build_link_for_note(self)
elixir.session.flush()
print("NOTE %s GOT LINK %s" % (self, self.link))
In the Link class I have
class Link(Entity):
. . .
#classmethod
def build_link_for_note(cls, note):
return Link(content='{"id": %d}' % note.id)
Both tables have autoincremented primary keys, so no worries there. The error that I get with this code is:
File ".../sqlalchemy/orm/session.py", line 1469, in flush
raise sa_exc.InvalidRequestError("Session is already flushing")
InvalidRequestError: Session is already flushing
I'll buy that. The #after_insert event gets called (I think) after the Note got stored to the database, which happened during the current session flush. And of course if I remove the elixir.session.flush() call, then of course it prints
NOTE <Note id:4 name:Danielle> GOT LINK <id:None content:{"t": 4}>
which again makes sense since I haven't been able to persist the link!
So my question is, how can I, create both a Note and a Link in a single request, so that the mutually dependent ids are available and properly recorded?
P.S. I understand that the schema here is a little unusal, and that I can solve this issue by either (1) spawning a task to create the Link asynchronously or (2) making the Link.content method create the link lazily. These solutions require some concurrency attention, so I am really hoping that a simple, direct SQLAlchemy solution with one session can work.
I'd advise against using Elixir's methods such as "save()" which mis-uses SQLAlchemy's API. Here is the aforementioned approach using standard SQLAlchemy events. Everything is achieved in one flush as well.
from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import event
import json
Base = declarative_base()
class Note(Base):
__tablename__ = "note"
id = Column(Integer, primary_key=True)
name = Column(String)
note_id = Column(Integer, ForeignKey('link.id'))
link = relationship("Link")
# if using __init__ here is distasteful to you,
# feel free to use the "init" event illustrated
# below instead
def __init__(self, name):
self.name = name
self.link = Link()
class Link(Base):
__tablename__ = "link"
id = Column(Integer, primary_key=True)
content = Column(String)
# using an event instead of Note.__init__
##event.listens_for(Note, "init")
#def init(target, args, kwargs):
# target.link = Link()
#event.listens_for(Note, "after_insert")
def after_insert(mapper, connection, target):
connection.execute(
Link.__table__.update().\
values(content=json.dumps({"t": target.id}))
)
e = create_engine("sqlite://", echo=True)
Base.metadata.create_all(e)
s = Session(e)
note = Note('Danielle')
s.add(note)
s.commit()
note = s.query(Note).first()
assert s.query(Link.content).scalar() == ('{"t": %d}' % note.id)
Since both objects have autogenerated IDs that come from the DB and want to store each other's IDs, you need to save both objects first, then save one of the objects once more, with the updated ID of other object.
So I'd go with removing the flush call and maybe calling save explicitly for each of the objects involved.