1.在PasteDeploy部署caesar-api服务时，setup_app中建立app，app中设置hooks，hooks负责加载conf配置文件和数据库连接 self.storage_connection。
从而在请求访问时可以调用对应钩子对象的方法。
def setup_app(pecan_config=None, extra_hooks=None):
# FIXME: Replace DBHook with a hooks.TransactionHook
app_hooks = [hooks.ConfigHook(CONF),
hooks.DBHook(CONF)]
# 配置文件钩子ConfigHook和数据库连接DBHook钩子。
if extra_hooks:
app_hooks.extend(extra_hooks)
if not pecan_config:
pecan_config = get_pecan_config()
pecan.configuration.set_config(dict(pecan_config), overwrite=True)
# NOTE(sileht): pecan debug won't work in multi-process environment
pecan_debug = CONF.api.pecan_debug
if CONF.api.workers and CONF.api.workers != 1 and pecan_debug:
pecan_debug = False
app = pecan.make_app(
pecan_config.app.root,
debug=pecan_debug,
force_canonical=getattr(pecan_config.app, 'force_canonical', True),
hooks=app_hooks, #添加请求钩子
wrap_app=middleware.ParsableErrorMiddleware,
guess_content_type_from_ext=False
)
return app
在DBHook中，before方法RoutingState中添加数据库连接属性storage_conn：从而在pecan.requst.storage_conn获取数据库连接
class DBHook(hooks.PecanHook):
def __init__(self, conf):
self.storage_connection = self.get_connection(conf)
if not self.storage_connection:
raise Exception(
"API failed to start. Failed to connect to database")
def before(self, state):
# 添加数据库连接
state.request.storage_conn = self.storage_connection
@staticmethod
def get_connection(conf):
try:
return storage.get_connection_from_config(conf)
except Exception as err:
LOG.exception("Failed to connect to db" "retry later: %s",
err)
通过debug：
在请求时无法使用pdb进行debug断点测试，需要在代码中设置import pdb;pdb.set_trace()同时，使用gdb attach 服务进程，然后再发送请求时，才会自动到断点位置。
2.请求访问（pecan对象路由框架）
在根目录root.py中定义v2对象，路由到V2Controller
class RootController(object):
def __init__(self):
self.v2 = v2.V2Controller()
在V2Controller中定义_look_up方法，对/v2/后的字段判断，如果为meters则路由到 meters.MetersController()对象
class V2Controller(rest.RestController):
@pecan.expose()
def _lookup(self, kind, *remainder):
if kind == 'meters':
return meters.MetersController(), remainder
meters.MetersController()又路由到 MeterController(meter_name)，其中的meter_name作为meters后的另一个参数。如果懂得springmvc的controller的requestMapping中路径映射，其类似于
@RequestMapping(value = "/xxx/{xxx}",method=RequestMethod.GET)中{xxx}动态获取请求中的变量
class MetersController(rest.RestController):
"""Works on meters."""
@pecan.expose()
def _lookup(self, meter_name, *remainder):
return MeterController(meter_name), remainder
在 MeterController(meter_name)中 GET请求被路由到get_all方法中，@wsme_pecan.wsexpose([OldSample], [base.Query], int)对请求参数和相应返回进行转化，返回值为list的OldSample对象，第一个参数为list的base.Query对象可以为None，limit 是int类型，可为None
class MeterController(rest.RestController):
"""Manages operations on a single meter."""
_custom_actions = {
'statistics': ['GET'],
}
def __init__(self, meter_name):
pecan.request.context['meter_name'] = meter_name
self.meter_name = meter_name
@wsme_pecan.wsexpose([OldSample], [base.Query], int)
def get_all(self, q=None, limit=None):
"""Return samples for the meter.
:param q: Filter rules for the data to be returned.
:param limit: Maximum number of samples to return.
"""
q = q or []
limit = v2_utils.enforce_limit(limit)
kwargs = v2_utils.query_to_kwargs(q, storage.SampleFilter.__init__)
kwargs['meter'] = self.meter_name
f = storage.SampleFilter(**kwargs)
return [OldSample.from_db_model(e)
for e in pecan.request.storage_conn.get_samples(f, limit=limit) # 数据库连接对象，调用其get_samples获取数据库数据
]
最后调用接口，查询数据库数据：
1.启动caesar-api服务：
2.调用/v2/meters接口获取数据
以上只是个人感悟，具体可参考我的github: https://github.com/CaesarLinsa/ceilometer_TestCase