返回float（value）ValueError：在Django模型中无法将字符串转换为float [英] return float(value) ValueError: could not convert string to float in Django models

问题描述

我尝试在此Django模型上进行迁移/迁移：

从django.db导入模型
从myapp .models导入站点

类GscElement（models.Model）：
ctr = models.FloatField（'Taux de clic'，默认= 0.0）
印象= models.IntegerField（ 'Nombre d\'impressions'，默认值= 0）
位置= models.FloatField（'Position moyenne'，默认值= 0.0）
点击次数= models.IntegerField（'Nombre de clics'，默认值= 0）
site = models.ForeignKey（
Site，
models.SET_NULL，
blank = True，
null = True
）

类Page（GscElement）：
page_field = models.TextField（'Url de la page'，default =''）
startdate = models.DateField（'Date du首发日期'，null = True）
enddate = models.DateField（'Date de fin'，null = True）

class Meta：
unique_together =（（（'startdate'，'enddate'，' page_field'，））

类别查询（GscElement）：
que ry_field = models.TextField（'Requête'，default =''）
startdate = models.DateField（'Date du premier'，null = True）
enddate = models.DateField（'Date de fin' ，null = True）

class Meta：
unique_together =（（'startdate'，'enddate'，'query_field'），）


，我得到这个错误：

 正在应用gsc。 0004_auto_20171024_1916 ...跟踪（最近一次通话最近）：
文件 manage.py，第22行，在< module>中
 execute_from_command_line（sys.argv）
文件 /Users/Quentin/git/myapp/myapp_env/lib/python3.6/site-packages/django/core/management/__init__.py，行364 ，在execute_from_command_line 
 utility.execute（）
文件 /Users/Quentin/git/myapp/myapp_env/lib/python3.6/site-packages/django/core/management/__init__.py中，第356行，在执行
 self.fetch_command（subcommand）.run_from_argv（self.argv）
 File /Users/Quentin/git/myapp/myapp_env/lib/python3.6/site-packages/django /core/management/base.py，第283行，位于run_from_argv 
 self.execute（* args，** cmd_options）
文件 / Users / Quentin / git / myapp / myapp_env / lib / python3 .6 / site-packages / django / core / management / base.py，行330，在执行
输出= self.handle（* args，** options）
文件 / Users / Quentin /git/myapp/myapp_env/lib/python3.6/site-packages/django/core/management/commands/migrate.py，第204行，句柄
 fake_initial = fake_initial，
文件 /用户/ Quentin / git / myapp / myap p_env / lib / python3.6 / site-packages / django / db / migrations / executor.py，行115，在迁移
状态= self._migrate_all_forwards（状态，计划，full_plan，fake = fake，fake_initial = fake_initial）
文件 /Users/Quentin/git/myapp/myapp_env/lib/python3.6/site-packages/django/db/migrations/executor.py，第145行，处于_migrate_all_forwards 
状态= self.apply_migration（状态，迁移，fake = fake，fake_initial = fake_initial）
文件 /Users/Quentin/git/myapp/myapp_env/lib/python3.6/site-packages/django/db/migrations/ executor.py，第244行，位于apply_migration 
 state = migration.apply（state，schema_editor）
文件 /Users/Quentin/git/myapp/myapp_env/lib/python3.6/site-packages /django/db/migrations/migration.py，第129行，应用
 operation.database_forwards（self.app_label，schema_editor，old_state，project_state）
文件 / Users / Quentin / git / myapp / myapp_env / lib / python3.6 / site-packages / django / db / migrations / operations / fields.py，第87行，在database_for中病房
字段，
文件 /Users/Quentin/git/myapp/myapp_env/lib/python3.6/site-packages/django/db/backends/sqlite3/schema.py，第238行，在add_field 
 self._remake_table（model，create_field = field）
文件 /Users/Quentin/git/myapp/myapp_env/lib/python3.6/site-packages/django/db/backends/sqlite3 /schema.py，第113行，位于_remake_table 
 self.effective_default（create_field）
文件 /Users/Quentin/git/myapp/myapp_env/lib/python3.6/site-packages/django/ db / backends / base / schema.py，第229行，位于valid_default 
中，默认= field.get_db_prep_save（默认，self.connection）
文件 / Users / Quentin / git / myapp / myapp_env / lib /python3.6/site-packages/django/db/models/fields/__init__.py，行770，在get_db_prep_save中
 prepare = False）
文件 / Users / Quentin / git / myapp / myapp_env / lib / python3.6 / site-packages / django / db / models / fields / __ init__.py，第762行，位于get_db_prep_value 
 value = self.get_prep_value（value）
 File / Users /昆汀/ git / myapp / myapp_env / lib / python3.6 / site-packages / django / db / models / fields / __ init__.py，行1781，在get_prep_value 
 return float（value）
 ValueError中：不将字符串转换为float：
  

您知道为什么吗？

仅供参考，我尝试恢复模型更改之前的数据库，并尝试压缩迁移，但始终会发生相同的错误。

谢谢！

编辑：我粘贴了所有回溯

解决方案

我不能肯定地说不看迁移文件。发布这些信息会有所帮助。也就是说，您似乎试图将ctr或position从字符串字段重命名为float字段。

这可能是在您执行makemigrations并询问您是否您重命名了一个字段。如果您不关心这些字段中的数据，则可以执行以下操作：

1. 删除该最新迁移


2. 再次恢复数据库


3. 再次运行python manage.py makemigrations


4. 当询问您是否重命名字段时，说

Django无法将字符串隐式转换为浮点数，因此如果您确实需要保留当前存储在您的数据中的模型，我建议如下：

1. 创建新的浮动字段2


2. 运行管理命令从一个字段获取数据，将其转换为float，然后将其保存到另一个字段


3. 删除第一个（字符串）字段


4. 将第二个字段（浮点字段）重命名为您需要的名称。

I try to makemigrations / migrate on this Django models :

from django.db import models
from myapp.models import Site

class GscElement(models.Model):
    ctr = models.FloatField('Taux de clic', default=0.0)
    impressions = models.IntegerField('Nombre d\'impressions', default=0)
    position = models.FloatField('Position moyenne', default=0.0)
    clicks = models.IntegerField('Nombre de clics', default=0)
    site = models.ForeignKey(
        Site,
        models.SET_NULL,
        blank=True,
        null=True
    )

class Page(GscElement):
    page_field = models.TextField('Url de la page', default='')
    startdate = models.DateField('Date du debut', null=True)
    enddate = models.DateField('Date de fin', null=True)

    class Meta:
        unique_together = (('startdate', 'enddate', 'page_field',))

class Query(GscElement):
    query_field = models.TextField('Requête', default='')
    startdate = models.DateField('Date du debut', null=True)
    enddate = models.DateField('Date de fin', null=True)

    class Meta:
        unique_together = (('startdate', 'enddate', 'query_field'),)

and I get this error :

 Applying gsc.0004_auto_20171024_1916...Traceback (most recent call last):
  File "manage.py", line 22, in <module>
    execute_from_command_line(sys.argv)
  File "/Users/Quentin/git/myapp/myapp_env/lib/python3.6/site-packages/django/core/management/__init__.py", line 364, in execute_from_command_line
    utility.execute()
  File "/Users/Quentin/git/myapp/myapp_env/lib/python3.6/site-packages/django/core/management/__init__.py", line 356, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/Users/Quentin/git/myapp/myapp_env/lib/python3.6/site-packages/django/core/management/base.py", line 283, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/Users/Quentin/git/myapp/myapp_env/lib/python3.6/site-packages/django/core/management/base.py", line 330, in execute
    output = self.handle(*args, **options)
  File "/Users/Quentin/git/myapp/myapp_env/lib/python3.6/site-packages/django/core/management/commands/migrate.py", line 204, in handle
    fake_initial=fake_initial,
  File "/Users/Quentin/git/myapp/myapp_env/lib/python3.6/site-packages/django/db/migrations/executor.py", line 115, in migrate
    state = self._migrate_all_forwards(state, plan, full_plan, fake=fake, fake_initial=fake_initial)
  File "/Users/Quentin/git/myapp/myapp_env/lib/python3.6/site-packages/django/db/migrations/executor.py", line 145, in _migrate_all_forwards
    state = self.apply_migration(state, migration, fake=fake, fake_initial=fake_initial)
  File "/Users/Quentin/git/myapp/myapp_env/lib/python3.6/site-packages/django/db/migrations/executor.py", line 244, in apply_migration
    state = migration.apply(state, schema_editor)
  File "/Users/Quentin/git/myapp/myapp_env/lib/python3.6/site-packages/django/db/migrations/migration.py", line 129, in apply
    operation.database_forwards(self.app_label, schema_editor, old_state, project_state)
  File "/Users/Quentin/git/myapp/myapp_env/lib/python3.6/site-packages/django/db/migrations/operations/fields.py", line 87, in database_forwards
    field,
  File "/Users/Quentin/git/myapp/myapp_env/lib/python3.6/site-packages/django/db/backends/sqlite3/schema.py", line 238, in add_field
    self._remake_table(model, create_field=field)
  File "/Users/Quentin/git/myapp/myapp_env/lib/python3.6/site-packages/django/db/backends/sqlite3/schema.py", line 113, in _remake_table
    self.effective_default(create_field)
  File "/Users/Quentin/git/myapp/myapp_env/lib/python3.6/site-packages/django/db/backends/base/schema.py", line 229, in effective_default
    default = field.get_db_prep_save(default, self.connection)
  File "/Users/Quentin/git/myapp/myapp_env/lib/python3.6/site-packages/django/db/models/fields/__init__.py", line 770, in get_db_prep_save
    prepared=False)
  File "/Users/Quentin/git/myapp/myapp_env/lib/python3.6/site-packages/django/db/models/fields/__init__.py", line 762, in get_db_prep_value
    value = self.get_prep_value(value)
  File "/Users/Quentin/git/myapp/myapp_env/lib/python3.6/site-packages/django/db/models/fields/__init__.py", line 1781, in get_prep_value
    return float(value)
ValueError: could not convert string to float: 

Do you have any idea why ?

FYI I tried to restore the databased I had before my models changes and tried to squash migrations too, but the same error always occured.

Thank you !

EDIT : I pasted all the traceback

解决方案

I can't say for sure without seeing the migration files. Posting those would be helpful. That said, it looks like you tried to rename either ctr or position from a string field to a float field.

This probably happened when you ran makemigrations and it asked you if you renamed a field. If you don't care about the data in those fields, you can do the following:

1. Delete that latest migration
2. Restore the database again
3. Run python manage.py makemigrations again
4. When it asks you if you renamed a field, say no.

Django can't implicitly convert a string to a float, so if you do need to keep the data currently stored in your models, I'd suggest the following:

1. Creating a new float field2
2. Run a management command to get the data from one field, convert it to a float, and save it to the other field
3. Delete the first (string) field
4. Rename the second field (the float field) to whatever name you need it to have.

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