AutoField

An IntegerField that automatically increments according to available IDs. You usually won't need to use this directly; a primary key field will automatically be added to your model if you don't specify otherwise. See Automatic primary key fields.

BooleanField

A true/false field.

The admin represents this as a checkbox.

CharField

A string field, for small- to large-sized strings.

For large amounts of text, use TextField.

The admin represents this as an <input type="text"> (a single-line input).

CharField has an extra required argument, maxlength, the maximum length (in characters) of the field. The maxlength is enforced at the database level and in Django's validation.
CharField需要一个必须参数：maxlength，表示字段的最大长度。

CommaSeparatedIntegerField

A field of integers separated by commas. As in CharField, the maxlength argument is required.

DateField

A date field. Has a few extra optional arguments:

Argument	Description
auto_now	Automatically set the field to now every time the object is saved. Useful for "last-modified" timestamps. Note that the current date is always used; it's not just a default value that you can override.在字段每次保存时自动更新为当前时间。不能被用户覆盖更改。
auto_now_add	Automatically set the field to now when the object is first created. Useful for creation of timestamps. Note that the current date is always used; it's not just a default value that you can override.在字段首次创建时自动保存为当前时间。不能被用户覆盖更改。

The admin represents this as an <input type="text"> with a JavaScript calendar and a shortcut for "Today."

DateTimeField

A date and time field. Takes the same extra options as DateField.

The admin represents this as two <input type="text"> fields, with JavaScript shortcuts.
它将作为两个text表单域。

EmailField

A CharField that checks that the value is a valid e-mail address. This doesn't accept maxlength; its maxlength is automatically set to 75.
它没有maxlength属性，最大程度自动被设为75。

FileField

A file-upload field.

Has an extra required argument, upload_to, a local filesystem path to which files should be upload. This path may contain strftime formatting, which will be replaced by the date/time of the file upload (so that uploaded files don't fill up the given directory).

The admin represents this as an <input type="file"> (a file-upload widget).

Using a FileField or an ImageField (see below) in a model takes a few steps:

1. In your settings file, you'll need to define MEDIA_ROOT as the full path to a directory where you'd like Django to store uploaded files. (For performance, these files are not stored in the database.) Define MEDIA_URL as the base public URL of that directory. Make sure that this directory is writable by the Web server's user account.
2. Add the FileField or ImageField to your model, making sure to define the upload_to option to tell Django to which subdirectory of MEDIA_ROOT it should upload files.
3. All that will be stored in your database is a path to the file (relative to MEDIA_ROOT). You'll most likely want to use the convenience get_<fieldname>_url function provided by Django. For example, if your ImageField is called mug_shot, you can get the absolute URL to your image in a template with {{ object.get_mug_shot_url }}.

For example, say your MEDIA_ROOT is set to '/home/media', and upload_to is set to 'photos/%Y/%m/%d'. The '%Y/%m/%d' part of upload_to is strftime formatting; '%Y' is the four-digit year, '%m' is the two-digit month and '%d' is the two-digit day. If you upload a file on Jan. 15, 2007, it will be saved in the directory /home/media/photos/2007/01/15.

Note that whenever you deal with uploaded files, you should pay close attention to where you're uploading them and what type of files they are, to avoid security holes. Validate all uploaded files so that you're sure the files are what you think they are. For example, if you blindly let somebody upload files, without validation, to a directory that's within your Web server's document root, then somebody could upload a CGI or PHP script and execute that script by visiting its URL on your site. Don't allow that.

FilePathField

A field whose choices are limited to the filenames in a certain directory on the filesystem. Has three special arguments, of which the first is required:

Argument	Description
path	Required. The absolute filesystem path to a directory from which this FilePathField should get its choices. Example: "/home/images".
match	Optional. A regular expression, as a string, that FilePathField will use to filter filenames. Note that the regex will be applied to the base filename, not the full path. Example: "foo.*\.txt^", which will match a file called foo23.txt but not bar.txt or foo23.gif.
recursive	Optional. Either True or False. Default is False. Specifies whether all subdirectories of path should be included.

Of course, these arguments can be used together.

The one potential gotcha is that match applies to the base filename, not the full path. So, this example:

FilePathField(path="/home/images", match="foo.*", recursive=True)

...will match /home/images/foo.gif but not /home/images/foo/bar.gif because the match applies to the base filename (foo.gif and bar.gif).

FloatField

A floating-point number. Has two required arguments:

Argument	Description
max_digits	The maximum number of digits allowed in the number. 最长长度
decimal_places	The number of decimal places to store with the number. 小数位最长长度

For example, to store numbers up to 999 with a resolution of 2 decimal places, you'd use:

models.FloatField(..., max_digits=5, decimal_places=2)

And to store numbers up to approximately one billion with a resolution of 10 decimal places:

models.FloatField(..., max_digits=19, decimal_places=10)

The admin represents this as an <input type="text"> (a single-line input).

ImageField

Like FileField, but validates that the uploaded object is a valid image. Has two extra optional arguments, height_field and width_field, which, if set, will be auto-populated with the height and width of the image each time a model instance is saved.

Requires the Python Imaging Library.

IntegerField

An integer.

The admin represents this as an <input type="text"> (a single-line input).

IPAddressField

An IP address, in string format (i.e. "24.124.1.30").

The admin represents this as an <input type="text"> (a single-line input).

NullBooleanField

Like a BooleanField, but allows NULL as one of the options. Use this instead of a BooleanField with null=True.

The admin represents this as a <select> box with "Unknown", "Yes" and "No" choices.
在表单管理界面将显示为select 选项，有unknown、yes、no三个选项。

PhoneNumberField

A CharField that checks that the value is a valid U.S.A.-style phone number (in the format XXX-XXX-XXXX).
电话号码格式字段，格式为***-***-****

PositiveIntegerField

Like an IntegerField, but must be positive.
正整数字段

PositiveSmallIntegerField

Like a PositiveIntegerField, but only allows values under a certain (database-dependent) point.
正整数字段，但限定在数据库支持的范围之内。

SlugField

"Slug" is a newspaper term. A slug is a short label for something, containing only letters, numbers, underscores or hyphens. They're generally used in URLs.
slug时一个只含有字符、数字、下划线、连字符的字段，一般用于url。

In the Django development version, you can specify maxlength. If maxlength is not specified, Django will use a default length of 50. In previous Django versions, there's no way to override the length of 50.
默认最长程度为50

Implies db_index=True.

Accepts an extra option, prepopulate_from, which is a list of fields from which to auto-populate the slug, via JavaScript, in the object's admin form:？？？？？？

models.SlugField(prepopulate_from=("pre_name", "name"))

prepopulate_from doesn't accept DateTimeFields.

The admin represents SlugField as an <input type="text"> (a single-line input).

SmallIntegerField

Like an IntegerField, but only allows values under a certain (database-dependent) point.

TextField

A large text field.

The admin represents this as a <textarea> (a multi-line input).

TimeField

A time. Accepts the same auto-population options as DateField and DateTimeField.

The admin represents this as an <input type="text"> with some JavaScript shortcuts.

URLField

A field for a URL. If the verify_exists option is True (default), the URL given will be checked for existence (i.e., the URL actually loads and doesn't give a 404 response).
如果verify_exists被设定为true，给定的url地址会自动被检查是否存在

The admin represents this as an <input type="text"> (a single-line input).

USStateField

A two-letter U.S. state abbreviation.

The admin represents this as an <input type="text"> (a single-line input).

XMLField

A TextField that checks that the value is valid XML that matches a given schema. Takes one required argument, schema_path, which is the filesystem path to a RelaxNG schema against which to validate the field.

null

If True, Django will store empty values as NULL in the database. Default is False.
如果null属性被设为true，那么空值将在数据库中被保存为NULL

Note that empty string values will always get stored as empty strings, not as NULL -- so use null=True for non-string fields such as integers, booleans and dates.
需要注意的是，空字符串总是被保存为空值，而不是NULL，因此仅可对非字符串字段使用，如日期、布尔值、整数。

Avoid using null on string-based fields such as CharField and TextField unless you have an excellent reason. If a string-based field has null=True, that means it has two possible values for "no data": NULL, and the empty string. In most cases, it's redundant to have two possible values for "no data;" Django convention is to use the empty string, not NULL.
因此要避免对CharField、TextField等字符串类字段使用null属性，除非你有特殊目的。

blank

If True, the field is allowed to be blank.
如果设为true，字段允许为空。

Note that this is different than null. null is purely database-related, whereas blank is validation-related. If a field has blank=True, validation on Django's admin site will allow entry of an empty value. If a field has blank=False, the field will be required.
blank与null不同，blank对一个字段的验证环节起作用。

choices

An iterable (e.g., a list or tuple) of 2-tuples to use as choices for this field.

If this is given, Django's admin will use a select box instead of the standard text field and will limit choices to the choices given.

A choices list looks like this:

YEAR_IN_SCHOOL_CHOICES = (
    ('FR', 'Freshman'),
    ('SO', 'Sophomore'),
    ('JR', 'Junior'),
    ('SR', 'Senior'),
    ('GR', 'Graduate'),
)

The first element in each tuple is the actual value to be stored. The second element is the human-readable name for the option.

The choices list can be defined either as part of your model class:

class Foo(models.Model):
    GENDER_CHOICES = (
        ('M', 'Male'),
        ('F', 'Female'),
    )
    gender = models.CharField(maxlength=1, choices=GENDER_CHOICES)

or outside your model class altogether:

GENDER_CHOICES = (
    ('M', 'Male'),
    ('F', 'Female'),
)
class Foo(models.Model):
    gender = models.CharField(maxlength=1, choices=GENDER_CHOICES)

Finally, note that choices can be any iterable object -- not necessarily a list or tuple. This lets you construct choices dynamically. But if you find yourself hacking choices to be dynamic, you're probably better off using a proper database table with a ForeignKey. choices is meant for static data that doesn't change much, if ever.

core

For objects that are edited inline to a related object.

In the Django admin, if all "core" fields in an inline-edited object are cleared, the object will be deleted.

It is an error to have an inline-editable relation without at least one core=True field.

Please note that each field marked "core" is treated as a required field by the Django admin site. Essentially, this means you should put core=True on all required fields in your related object that is being edited inline.

db_column

The name of the database column to use for this field. If this isn't given, Django will use the field's name.
定义数据库表中的列名。

If your database column name is an SQL reserved word, or contains characters that aren't allowed in Python variable names -- notably, the hyphen -- that's OK. Django quotes column and table names behind the scenes.

db_index

If True, django-admin.py sqlindexes will output a CREATE INDEX statement for this field.
是否为本字段定义索引。

default

The default value for the field.

editable

If False, the field will not be editable in the admin or via form processing using the object's AddManipulator or ChangeManipulator classes. Default is True.

help_text

Extra "help" text to be displayed under the field on the object's admin form. It's useful for documentation even if your object doesn't have an admin form.

primary_key

If True, this field is the primary key for the model.

If you don't specify primary_key=True for any fields in your model, Django will automatically add this field:
如果你没有自己指定任何一个字段的primary_key属性为true，django会自动为你添加一个primary_key属性为true的字段id：

id = models.AutoField('ID', primary_key=True)

Thus, you don't need to set primary_key=True on any of your fields unless you want to override the default primary-key behavior.
因此，除非你有特殊需要，一般可以不必将一个字段的primary_key属性设置为true。

primary_key=True implies blank=False, null=False and unique=True. Only one primary key is allowed on an object.
如果一个字段的primary_key属性被设置为true，意味着blank=false,null=false,unique=true。一个模型中只能有自已字段primary_key属性为true。

radio_admin

By default, Django's admin uses a select-box interface (<select>) for fields that are ForeignKey or have choices set. If radio_admin is set to True, Django will use a radio-button interface instead.
默认情况下，django使用选项菜单显示那些foreignkey字段和设置有choices属性的字段，如果将radio_admin属性设置为true，将使用单选按钮显示。

Don't use this for a field unless it's a ForeignKey or has choices set.
只有在设置了foreignkey或choices集合的情况下，方可使用这个属性设置。

unique

If True, this field must be unique throughout the table.

This is enforced at the database level and at the Django admin-form level.

Set this to the name of a DateField or DateTimeField to require that this field be unique for the value of the date field.

unique_for_month

Like unique_for_date, but requires the field to be unique with respect to the month.
同unique_for_date。

unique_for_year

Like unique_for_date and unique_for_month.
同unique_for_date和unique_for_month。

validator_list

A list of extra validators to apply to the field. Each should be a callable that takes the parameters field_data, all_data and raises django.core.validators.ValidationError for errors. (See the validator docs.)
一个字段限制情况列表。具体参见validator docs

Django comes with quite a few validators. They're in django.core.validators.
django有许多限制器，它们存放在包django.core.validators下面。

Many-to-one relationships

To define a many-to-one relationship, use ForeignKey. You use it just like any other Field type: by including it as a class attribute of your model.
要定义一个多对一关系，可以在你的模型定义中，使用foreignkey类型字段。

ForeignKey requires a positional argument: The class to which the model is related.
foreignkey需要一个明确的指示：要关联的模型对象。

For example, if a Car model has a Manufacturer -- that is, a Manufacturer makes multiple cars but each Car only has one Manufacturer -- use the following definitions:
比如：car模型有一个属性manufacturer，一个供应商可以生产多种car，但一种car只能有一个供应商。他们之间的关系可以表示如下：

class Manufacturer(models.Model):
    # ...

class Car(models.Model):
    manufacturer = models.ForeignKey(Manufacturer)
    # ...

To create a recursive relationship -- an object that has a many-to-one relationship with itself -- use models.ForeignKey('self').

If you need to create a relationship on a model that has not yet been defined, you can use the name of the model, rather than the model object itself:

class Car(models.Model):
    manufacturer = models.ForeignKey('Manufacturer')
    # ...

class Manufacturer(models.Model):
    # ...

Note, however, that you can only use strings to refer to models in the same models.py file -- you cannot use a string to reference a model in a different application, or to reference a model that has been imported from elsewhere.
你可以使用字符串来表示还没有定义的其他model对象，但仅限于在同一个models文件内。

Behind the scenes, Django appends "_id" to the field name to create its database column name. In the above example, the database table for the Car model will have a manufacturer_id column. (You can change this explicitly by specifying db_column; see db_column below.) However, your code should never have to deal with the database column name, unless you write custom SQL. You'll always deal with the field names of your model object.

It's suggested, but not required, that the name of a ForeignKey field (manufacturer in the example above) be the name of the model, lowercase. You can, of course, call the field whatever you want. For example:

class Car(models.Model):
    company_that_makes_it = models.ForeignKey(Manufacturer)
    # ...

See the Many-to-one relationship model example for a full example.

ForeignKey fields take a number of extra arguments for defining how the relationship should work. All are optional:

Argument	Description
edit_inline	If not False, this related object is edited "inline" on the related object's page. This means that the object will not have its own admin interface. Use either models.TABULAR or models.STACKED, which, respectively, designate whether the inline-editable objects are displayed as a table or as a "stack" of fieldsets.？？？？？？
limit_choices_to	A dictionary of lookup arguments and values (see the Database API reference) that limit the available admin choices for this object. Use this with models.LazyDate to limit choices of objects by date. For example: limit_choices_to = {'pub_date__lte': models.LazyDate()} only allows the choice of related objects with a pub_date before the current date/time to be chosen.？？？？？？ Instead of a dictionary this can also be a Q object (an object with a get_sql() method) for more complex queries. Not compatible with edit_inline.
max_num_in_admin	For inline-edited objects, this is the maximum number of related objects to display in the admin. Thus, if a pizza could only have up to 10 toppings, max_num_in_admin=10 would ensure that a user never enters more than 10 toppings. Note that this doesn't ensure more than 10 related toppings ever get created. It simply controls the admin interface; it doesn't enforce things at the Python API level or database level.
min_num_in_admin	The minimum number of related objects displayed in the admin. Normally, at the creation stage, num_in_admin inline objects are shown, and at the edit stage num_extra_on_change blank objects are shown in addition to all pre-existing related objects. However, no fewer than min_num_in_admin related objects will ever be displayed.
num_extra_on_change	The number of extra blank related-object fields to show at the change stage.
num_in_admin	The default number of inline objects to display on the object page at the add stage.
raw_id_admin	Only display a field for the integer to be entered instead of a drop-down menu. This is useful when related to an object type that will have too many rows to make a select box practical. Not used with edit_inline.
related_name	The name to use for the relation from the related object back to this one. See the related objects documentation for a full explanation and example.
to_field	The field on the related object that the relation is to. By default, Django uses the primary key of the related object.

Many-to-many relationships

To define a many-to-many relationship, use ManyToManyField. You use it just like any other Field type: by including it as a class attribute of your model.

ManyToManyField requires a positional argument: The class to which the model is related.

For example, if a Pizza has multiple Topping objects -- that is, a Topping can be on multiple pizzas and each Pizza has multiple toppings -- here's how you'd represent that:

class Topping(models.Model):
    # ...

class Pizza(models.Model):
    # ...
    toppings = models.ManyToManyField(Topping)

As with ForeignKey, a relationship to self can be defined by using the string 'self' instead of the model name, and you can refer to as-yet undefined models by using a string containing the model name. However, you can only use strings to refer to models in the same models.py file -- you cannot use a string to reference a model in a different application, or to reference a model that has been imported from elsewhere.

It's suggested, but not required, that the name of a ManyToManyField (toppings in the example above) be a plural describing the set of related model objects.

Behind the scenes, Django creates an intermediary join table to represent the many-to-many relationship.

It doesn't matter which model gets the ManyToManyField, but you only need it in one of the models -- not in both.

Generally, ManyToManyField instances should go in the object that's going to be edited in the admin interface, if you're using Django's admin. In the above example, toppings is in Pizza (rather than Topping having a pizzas ManyToManyField ) because it's more natural to think about a Pizza having toppings than a topping being on multiple pizzas. The way it's set up above, the Pizza admin form would let users select the toppings.

See the Many-to-many relationship model example for a full example.

ManyToManyField objects take a number of extra arguments for defining how the relationship should work. All are optional:

Argument	Description
related_name	See the description under ForeignKey above.
filter_interface	Use a nifty unobtrusive Javascript "filter" interface instead of the usability-challenged <select multiple> in the admin form for this object. The value should be models.HORIZONTAL or models.VERTICAL (i.e. should the interface be stacked horizontally or vertically).
limit_choices_to	See the description under ForeignKey above.
symmetrical	Only used in the definition of ManyToManyFields on self. Consider the following model: class Person(models.Model): friends = models.ManyToManyField("self") When Django processes this model, it identifies that it has a ManyToManyField on itself, and as a result, it doesn't add a person_set attribute to the Person class. Instead, the ManyToManyField is assumed to be symmetrical -- that is, if I am your friend, then you are my friend. If you do not want symmetry in ManyToMany relationships with self, set symmetrical to False. This will force Django to add the descriptor for the reverse relationship, allowing ManyToMany relationships to be non-symmetrical.

One-to-one relationships

The semantics of one-to-one relationships will be changing soon, so we don't recommend you use them. If that doesn't scare you away, keep reading.

To define a one-to-one relationship, use OneToOneField. You use it just like any other Field type: by including it as a class attribute of your model.

This is most useful on the primary key of an object when that object "extends" another object in some way.

OneToOneField requires a positional argument: The class to which the model is related.

For example, if you're building a database of "places", you would build pretty standard stuff such as address, phone number, etc. in the database. Then, if you wanted to build a database of restaurants on top of the places, instead of repeating yourself and replicating those fields in the Restaurant model, you could make Restaurant have a OneToOneField to Place (because a restaurant "is-a" place).

As with ForeignKey, a relationship to self can be defined by using the string "self" instead of the model name; references to as-yet undefined models can be made by using a string containing the model name.

This OneToOneField will actually replace the primary key id field (since one-to-one relations share the same primary key), and will be displayed as a read-only field when you edit an object in the admin interface:

See the One-to-one relationship model example for a full example.

class Admin:
    fields = (
        (None, {
            'fields': ('url', 'title', 'content', 'sites')
        }),
        ('Advanced options', {
            'classes': 'collapse',
            'fields' : ('enable_comments', 'registration_required', 'template_name')
        }),
    )

fields

A tuple of field names to display in this fieldset. This key is required.

Example:

{
'fields': ('first_name', 'last_name', 'address', 'city', 'state'),
}

To display multiple fields on the same line, wrap those fields in their own tuple. In this example, the first_name and last_name fields will display on the same line:

{
'fields': (('first_name', 'last_name'), 'address', 'city', 'state'),
}

classes

A string containing extra CSS classes to apply to the fieldset.

Example:

{
'classes': 'wide',
}

Apply multiple classes by separating them with spaces. Example:

{
'classes': 'wide extrapretty',
}

Two useful classes defined by the default admin-site stylesheet are collapse and wide. Fieldsets with the collapse style will be initially collapsed in the admin and replaced with a small "click to expand" link. Fieldsets with the wide style will be given extra horizontal space.

description

A string of optional extra text to be displayed at the top of each fieldset, under the heading of the fieldset. It's used verbatim, so you can use any HTML and you must escape any special HTML characters (such as ampersands) yourself.

Adding extra Manager methods

Adding extra Manager methods is the preferred way to add "table-level" functionality to your models. (For "row-level" functionality -- i.e., functions that act on a single instance of a model object -- use Model methods, not custom Manager methods.)

A custom Manager method can return anything you want. It doesn't have to return a QuerySet.

For example, this custom Manager offers a method with_counts(), which returns a list of all OpinionPoll objects, each with an extra num_responses attribute that is the result of an aggregate query:

class PollManager(models.Manager):
    def with_counts(self):
        from django.db import connection
        cursor = connection.cursor()
        cursor.execute("""
            SELECT p.id, p.question, p.poll_date, COUNT(*)
            FROM polls_opinionpoll p, polls_response r
            WHERE p.id = r.poll_id
            GROUP BY 1, 2, 3
            ORDER BY 3 DESC""")
        result_list = []
        for row in cursor.fetchall():
            p = self.model(id=row[0], question=row[1], poll_date=row[2])
            p.num_responses = row[3]
            result_list.append(p)
        return result_list

class OpinionPoll(models.Model):
    question = models.CharField(maxlength=200)
    poll_date = models.DateField()
    objects = PollManager()

class Response(models.Model):
    poll = models.ForeignKey(Poll)
    person_name = models.CharField(maxlength=50)
    response = models.TextField()

With this example, you'd use OpinionPoll.objects.with_counts() to return that list of OpinionPoll objects with num_responses attributes.

Another thing to note about this example is that Manager methods can access self.model to get the model class to which they're attached.

Modifying initial Manager QuerySets

A Manager's base QuerySet returns all objects in the system. For example, using this model:

class Book(models.Model):
    title = models.CharField(maxlength=100)
    author = models.CharField(maxlength=50)

...the statement Book.objects.all() will return all books in the database.

You can override a Manager's base QuerySet by overriding the Manager.get_query_set() method. get_query_set() should return a QuerySet with the properties you require.

For example, the following model has two Managers -- one that returns all objects, and one that returns only the books by Roald Dahl:

# First, define the Manager subclass.
class DahlBookManager(models.Manager):
    def get_query_set(self):
        return super(DahlBookManager, self).get_query_set().filter(author='Roald Dahl')

# Then hook it into the Book model explicitly.
class Book(models.Model):
    title = models.CharField(maxlength=100)
    author = models.CharField(maxlength=50)

    objects = models.Manager() # The default manager.
    dahl_objects = DahlBookManager() # The Dahl-specific manager.

With this sample model, Book.objects.all() will return all books in the database, but Book.dahl_objects.all() will only return the ones written by Roald Dahl.

Of course, because get_query_set() returns a QuerySet object, you can use filter(), exclude() and all the other QuerySet methods on it. So these statements are all legal:

Book.dahl_objects.all()
Book.dahl_objects.filter(title='Matilda')
Book.dahl_objects.count()

This example also pointed out another interesting technique: using multiple managers on the same model. You can attach as many Manager() instances to a model as you'd like. This is an easy way to define common "filters" for your models.

For example:

class MaleManager(models.Manager):
    def get_query_set(self):
        return super(MaleManager, self).get_query_set().filter(sex='M')

class FemaleManager(models.Manager):
    def get_query_set(self):
        return super(FemaleManager, self).get_query_set().filter(sex='F')

class Person(models.Model):
    first_name = models.CharField(maxlength=50)
    last_name = models.CharField(maxlength=50)
    sex = models.CharField(maxlength=1, choices=(('M', 'Male'), ('F', 'Female')))
    people = models.Manager()
    men = MaleManager()
    women = FemaleManager()

This example allows you to request Person.men.all(), Person.women.all(), and Person.people.all(), yielding predictable results.

If you use custom Manager objects, take note that the first Manager Django encounters (in order by which they're defined in the model) has a special status. Django interprets the first Manager defined in a class as the "default" Manager. Certain operations -- such as Django's admin site -- use the default Manager to obtain lists of objects, so it's generally a good idea for the first Manager to be relatively unfiltered. In the last example, the people Manager is defined first -- so it's the default Manager.