ietf-netmod-yang - 删除具有默认值的叶子（阳）

Question

说我有这个

container c {
  leaf l1;
  leaf l2 (default 'abcd');
}

我这样做（restconf）：

删除 /c/l2

服务器中的预期行为是什么？是吗

• '删除叶子数据' 或
• '不要删除但保留默认值的叶子'

发出 delete 后，GET 的预期结果是什么

GET /c
c {
  l1 : 100 // for ex
  l2 : 'abcd'
}

Answer 1

这在RFC7950 第 7.6.1 节中有描述：

The default value of a leaf is the value that the server uses if the

leaf does not exist in the data tree.  The usage of the default value
depends on the leaf's closest ancestor node in the schema tree that
is not a non-presence container (see Section 7.5.1):

  o  If no such ancestor exists in the schema tree, the default value

     MUST be used.

  o  Otherwise, if this ancestor is a case node, the default value MUST

     be used if any node from the case exists in the data tree or the
     case node is the choice's default case, and if no nodes from any
     other case exist in the data tree.

  o  Otherwise, the default value MUST be used if the ancestor node

     exists in the data tree.

In these cases, the default value is said to be in use.

Note that if the leaf or any of its ancestors has a "when" condition

or "if-feature" expression that evaluates to "false", then the
default value is not in use.

When the default value is in use, the server MUST operationally

behave as if the leaf was present in the data tree with the default
value as its value.

If a leaf has a "default" statement, the leaf's default value is the

value of the "default" statement.  Otherwise, if the leaf's type has
a default value and the leaf is not mandatory, then the leaf's
default value is the type's default value.  In all other cases, the
leaf does not have a default value.

在您的情况下c是一个不存在的容器，因此上面的第一个项目符号启动。这意味着如果您从数据树中删除相应的叶子（是的，您可以删除它），您的默认值将被使用。因此，服务器必须在操作上表现得好像叶子存在一样，并且这个叶子必须具有指定的默认值。

使用哪种协议来执行操作并不重要。

对于 RESTCONF 和 GET，行为在第 3.5.4 节中描述：

RESTCONF requires that a server report its default handling mode (see

Section 9.1.2 for details).  If the optional "with-defaults" query
parameter is supported by the server, a client may use it to control
retrieval of default values (see Section 4.8.9 for details).

If a leaf or leaf-list is missing from the configuration and there is

a YANG-defined default for that data resource, then the server MUST
use the YANG-defined default as the configured value.

If the target of a GET method is a data node that represents a leaf

or leaf-list that has a default value, and the leaf or leaf-list has
not been instantiated yet, the server MUST return the default
value(s) that are in use by the server.  In this case, the server
MUST ignore its basic-mode, described in Section 4.8.9, and return
the default value.

If the target of a GET method is a data node that represents a

container or list that has any child resources with default values,
for the child resources that have not been given value yet, the
server MAY return the default values that are in use by the server,
in accordance with its reported default handing mode and query
parameters passed by the client.

因此，正如上面最后一段所暗示的，您的 GET 示例可能正确也可能不正确，具体取决于有效的默认处理模式。