I have a timestamp field in a table and when i create a new instance of my object, set some fields, do not set the timestamp field and use the .Save(), i get an error saying that i cannot set an exlicite value to a timestamp field during an INSERT.
How can i have SubSonic not save anything in that perticular field?
Thank you
I'm not sure I perfectly understand the question, but the default SubSonic templates are set up to treat certain date/time fields as special cases, those being CreatedOn and ModifiedOn. You could look through your T4 template for references to those fields and modify their behavior.
Does this even apply to your situation, or are your timestamp fields named something else completely?
this is what you are looking for
http://mvcframeworkblog.blogspot.com/2009/10/subsonic-how-to-add-new-datatype.html
Related
I have legacy code which had no foreign keys defined in the schema.
The raw data for the row includes the key value of the parent, naturally.
My first porting attempt to postgresql just updated the field with the raw value: I did not add foreign keys to Django's models.
Now I am trying to add foreign keys to make the schema more informative.
When I add a foreign key, django's update requires me to provide an instance of the parent object: I can no longer update by simply providing the key value. But this is onerous because now I need to include in my code knowledge of all the relations to go and fetch related objects, and have specific update calls per model. This seems crazy to me, at least starting from where I am, so I feel like I am really missing something.
Currently, the update code just pushes rows in blissful ignorance. The update code is generic for tables, which is easy when there are no relations.
Django's model data means that I can find the related object dynamically for any given model, and doing this means I can still keep very abstracted table update logic. So this is what I am thinking of doing. Or just doing raw SQL updates.
Does a solution to this already exist, even if I can't find it? I am expecting to be embarrassed.
The ValueError comes in django ORM code which knows exactly which model it expects and what the related field is: the missing step if to find the instance of related object.
db.models.fields.related_descriptors.py:
in this code, which throws the exception, value is supposed to be an instance of the parent model. Instead, value is the key value. This basically I think tells me how I can inspect the model to deal with this in advance, but I wonder if I am re-inventing the wheel.
if value is not None and not isinstance(value, self.field.remote_field.model._meta.concrete_model):
raise ValueError(
'Cannot assign "%r": "%s.%s" must be a "%s" instance.' % (
value,
instance._meta.object_name,
self.field.name,
self.field.remote_field.model._meta.object_name,
)
)
You could use _id suffix to set id value directly
For given model
class Album(models.Model):
artist = models.ForeignKey(Musician, on_delete=models.CASCADE)
You can set artist by id in following manner
Album.objects.create(artist_id=2)
I have a boolean atrribute whose default is false. How can i get the date when the attribute was changed to true?
The is_changed gives you if the value was changed. I want the date when the attribute was first changed.
How do i get it in rails?
add attribute 'first_change' in that table which will save time stamp of every first change of the boolean attribute changed to true or false, then in model write the callback like this
before_update :check_changes
def check_changes
if self.<boolean_attribute>.is_changed? and first_change.nil?
self.update(first_change: Time.now)
end
end
After this you can check when the boolean attribute was changed.
You can wrap your boolean attribute in distinct model and from there you can easily trace when specific field was initially setted up or updated. In your current model you can't trace changing state of specific attributes, only the whole object, but it's not what you need I guess.
Well, looks like you basically want the feature of git in ActiveRecord records.
There are two ways
Use a separate col like changed_date. Update it whenever the field is changed for the first time.
I recommend this if your requirement is that simple. Do not use heavier gems.
Use libraries like VestalVersion or PaperTrail
these are helpful to track every activity in your records.
you can keep track of every changes, what its changed to and when
also you can revert your record to any point of time it was changed
I think there are two ways like above answer suggested to make a separate field and add date there when field changed first time or
you can use Public Activity gem that will log all the model activity with params.
It creates a activities table based on this table you can get the date of the fields when it was first changed but it is a lengthy process
I am still quite new to Yesod so I might be missing something essential.
My understanding is that adding the Maybe attribute to a Persist Entity field seems to both make the attribute non nullable in the database as well as wrapping it in a Maybe in the Data definition. I tried creating a test Entity with a timestamp that has a default=CURRENT_TIME. If I now send a JSON representation of this entity without the timestamp, I get an error about the missing timestamp when I try to use requireJsonBody. I guess I could add Maybe to the timestamp to get the JSON parsing to succeed. But then I would not have the non null constraint for the column in the database anymore?
Whenever I create a new activity, I need a date field to be autopopulated ( it will be autopopulated but greyed out until and unless a checkbox next to it needs to be checked).
I perform a validation based on the date field, when a new activity is created. since the date field check box is not checked, it is not considering the value for the validation.
Any help or suggestion is appreciated.
Thanks.
Jaya Vignesh.
make use of predefault and postdefault values to populate current-date.
set field Read-only (BC field user property). You can find it under Business Component in object explorer.
Field read-only allows you to make a field read-only based on value of other field from same BC or joined field.
I perform a validation based on the date field, when a new activity is created. since the date field check box is not checked, it is not considering the value for the validation.
This requirement of yours isn't clear what exactly you want to validate. Since you are populating it bydefault, I don't find the significance in validating your own auto-populated data. well yet I provide a suggestion below
There are two types of validations, 1. Using configuration or 2. Using scripting. I am not pretty much sure if it can be achieved with configuration but scripting it is possible by overriding BusComp_presetFieldValue, BusComp_preWriteValue. The first one executed when you populate a field. And the latter one when you commit the record.
I have answer assuming your requirement. Let me know if you have any questions or clarifications required.
You can add the Predefault property of the field to be the following
System: TimeStamp
I have two threads, one which runs something like update t set ColA=foo and the other runs update t set ColB=foo. If they were doing raw SQL statements there would be no contention, but since Django gets and saves the entire row, a race condition can occur.
Is there any way to tell Django that I just want to save a certain column?
Update old topic.
Now, we have update_fields argument with save:
If save() is passed a list of field names in keyword argument
update_fields, only the fields named in that list will be updated.
https://docs.djangoproject.com/en/stable/ref/models/instances/#specifying-which-fields-to-save
product.name = 'Name changed again'
product.save(update_fields=['name'])
You are correct that save will update the entire row but Django has an update which does exactly what you describe.
https://docs.djangoproject.com/en/stable/ref/models/querysets/#update
I think your only option to guarantee this is to write the raw SQL by hand by using Manager.raw() or a cursor depending on which one is more appropriate.