Is it obligatory to specify all the propertis of a attribute like this
#Column(name = "ID_COMPANY", unique = true, nullable = false)
or make just :
#Column(name = "ID_COMPANY")
and for a string we have to specify a length ?
#Column(name = "NAME", length = 30)
or just :
#Column(name = "NAME")
Because if i change the length of varchar in my database i have to change it again at my mapping class and it's little hard if i have many changes.
No, it's not obligatory.
Most of these options other than name are used only if you use Hibernate to generate your database schema. If you maintain your schema manually, you can safely omit them.
However, some of them (such as nullable or unique) may be useful for documentation purposes.
All the elements of the #Column annotation have default values. Unless your schema goes against the defaults in nullability, uniqueness, length, etc. (or your DB column does not exactly match the name of your field name), you can leave them off the annotation to prevent clutter.
Defaults can be seen on the JavaDoc here: http://docs.oracle.com/javaee/7/api/javax/persistence/Column.html
Related
Can I do the following to make a charfield unique and not null using tortoise orm?
class User(Model):
id = fields.IntField(pk = True)
username = fields.CharField(max_length = 128, unique = True, nullable = False)
Or what would be the appropriate field?
Is there a field for email type data? or which one should be used
Thank you!
The docs specify max_input and **kwargs as input parameters for CharField.
https://tortoise-orm.readthedocs.io/en/latest/fields.html#tortoise.fields.data.CharField
You can find the **kwargs for CharField in its parent class, the base Field.
https://tortoise-orm.readthedocs.io/en/latest/fields.html#tortoise.fields.base.Field
There you find parameters like:
null (bool) – Is this field nullable?
unique (bool) – Is this field unique?
validators (Optional[List[Union[Validator, Callable]]]) – Validators for this field.
See the docs for more info on how to use validators: https://tortoise-orm.readthedocs.io/en/latest/validators.html
i have two classes 'topics' and 'webpage' and i'm trying to assign webpage.category as a foreign key referencing to topics.top_name.
But unlike raw sql where a foreign key can reference to a particular field in another table, in django's orm we just provide the referenced class'(table's) name and not the particular field the FK is referrring to.
class Topic(models.Model):
top_name = models.CharField(max_length=264, unique=True)
top_author = models.CharField(max_length=264)
class Webpage(models.Model):
category = models.ForeignKey(Topic)
name = models.CharField(max_length=264)
url = models.URLField()
You can set the to_field=… [Django-doc] in the ForeignKey constructor:
class Topic(models.Model):
top_name = models.CharField(max_length=264, unique=True)
top_author = models.CharField(max_length=264)
class Webpage(models.Model):
category = models.ForeignKey(Topic, to_field='top_name', on_delete=models.CASCADE)
name = models.CharField(max_length=264)
url = models.URLField()
As specified in the documentation, the field to which you refer should be unique (which of course makes sense, since otherwise, it would be ambiguous).
Note that usually, the collation [mysql-doc] of the referencing column and the target column should be the same. Otherwise it is not completely clear when the two fields are equal.
If you do not specify the to_field, it will use the primary key of the target model.
i have a model attribute having the following
class ph_no(models.Model):
phone_no = models.CharField(max_length = 20)
phone_no_assigned_to = models.CharField(max_length = 50)
actually the value for the field phone_no_assigned_to should come from many tables in db like
personal_usage
bussiness_usage etc..
Each of the willl have assigned to field
Also this phone_no_assigned_to can have mutiple values
Can anyone help me how to define it
You might want to define relationships, i.e. have a model phone_usage with usage types and link it to model's ph_no field phone_no_assigned_to. Or if "usage" is a small list of possible values use choices.
Have a look at:
https://docs.djangoproject.com/en/1.9/topics/db/models/#relationships
https://docs.djangoproject.com/en/1.9/topics/db/examples/
https://docs.djangoproject.com/en/1.9/ref/models/fields/#choices
I have to work with a database containing columns with a dash in their name, as for example a-name. When converting the table with peewee, it converts it to an illegal character, with python complaining about a misplaced operator.
For a table with 2 columns, id and a-name, the result would be
from peewee import *
database = MySQLDatabase('databasename', **{'password': 'pwd', 'host': 'ip', 'user': 'username'})
class BaseModel(Model):
class Meta:
database = database
class ATable(BaseModel):
id = PrimaryKeyField()
a-name = CharField()
class Meta:
db_table = 'aTable'
I found a temporary workaround by changing the dash to an underscore and using the optional parameter db_column, like
a_name = CharField(db_column='a-name')
Is there another possibility for this issue as I do not want to do manual changes everytime I download the models from the database server?
I should add that I have no control over the database server, I have merely an account with read-only permissions.
Greetings,
Luc
a_name = CharField(db_column='a-name')
This is the correct way to solve the problem. Python does not allow dashes in identifiers, so if your column uses them then specify the column name explicitly and use a nice name for the column.
I suppose you could look into modifying the playhouse.reflection.Introspector.make_column_name method, as well.
I have a Spring application which uses JPA (Hibernate) initially created with Spring Roo. I need to store Strings with arbitrary length, so for that reason I've annotated the field with #Lob:
public class MyEntity{
#NotNull
#Size(min = 2)
#Lob
private String message;
...
}
The application works ok in localhost but I've deployed it to an external server and it a problem with encoding has appeared. For that reason I'd like to check if the data stored in the PostgreSQL database is ok or not. The application creates/updates the tables automatically. And for that field (message) it has created a column of type:
text NOT NULL
The problem is that after storing data if I browse the table or just do a SELECT of that column I can't see the text but numbers. Those numbers seems to be identifiers to "somewhere" where that information is stored.
Can anyone tell me exactly what are these identifiers and if there is any way of being able to see the stored data in a #Lob columm from a pgAdmin or a select clause?
Is there any better way to store Strings of arbitrary length in JPA?
Thanks.
I would recommend skipping the '#Lob' annotation and use columnDefinition like this:
#Column(columnDefinition="TEXT")
see if that helps viewing the data while browsing the database itself.
Use the #LOB definition, it is correct. The table is storing an OID to the catalogs -> postegreSQL-> tables -> pg_largeobject table.
The binary data is stored here efficiently and JPA will correctly get the data out and store it for you with this as an implementation detail.
Old question, but here is what I found when I encountered this:
http://www.solewing.org/blog/2015/08/hibernate-postgresql-and-lob-string/
Relevant parts below.
#Entity
#Table(name = "note")
#Access(AccessType.FIELD)
class NoteEntity {
#Id
private Long id;
#Lob
#Column(name = "note_text")
private String noteText;
public NoteEntity() { }
public NoteEntity(String noteText) { this.noteText = noteText }
}
The Hibernate PostgreSQL9Dialect stores #Lob String attribute values by explicitly creating a large object instance, and then storing the UID of the object in the column associated with attribute.
Obviously, the text of our notes isn’t really in the column. So where is it? The answer is that Hibernate explicitly created a large object for each note, and stored the UID of the object in the column. If we use some PostgreSQL large object functions, we can retrieve the text itself.
Use this to query:
SELECT id,
convert_from(loread(
lo_open(note_text::int, x'40000'::int), x'40000'::int), 'UTF-8')
AS note_text
FROM note