KONG DB抽象

function DB.new(kong_config, strategy)

if not kong_config then

error("missing kong_config", 2)

end

if strategy ~= nil and type(strategy) ~= "string" then

error("strategy must be a string", 2)

end

strategy = strategy or kong_config.database

-- load errors

local errors = Errors.new(strategy)

local schemas = {}

do

-- load schemas

-- core entities are for now the only source of schemas.

-- TODO: support schemas from plugins entities as well.

for _, entity_name in ipairs(constants.CORE_ENTITIES) do

local entity_schema = require("kong.db.schema.entities." .. entity_name)

-- validate core entities schema via metaschema

local ok, err_t = MetaSchema:validate(entity_schema)

if not ok then

return nil, fmt("schema of entity '%s' is invalid: %s", entity_name,

tostring(errors:schema_violation(err_t)))

end

local entity, err = Entity.new(entity_schema)

if not entity then

return nil, fmt("schema of entity '%s' is invalid: %s", entity_name,

err)

end

schemas[entity_name] = entity

-- load core entities subschemas

local subschemas

ok, subschemas = utils.load_module_if_exists("kong.db.schema.entities." .. entity_name .. "_subschemas")

if ok then

for name, subschema in pairs(subschemas) do

local ok, err = entity:new_subschema(name, subschema)

if not ok then

return nil, ("error initializing schema for %s: %s"):format(entity_name, err)

end

end

end

end

end

-- load strategy

//按照配置，构造返回特定类型数据库的连接器，针对每个实体对象的底层访问对像的字典strategies

local connector, strategies, err = Strategies.new(kong_config, strategy,

schemas, errors)

if err then

return nil, err

end

local daos = {}

local self = {

daos = daos, -- each of those has the connector singleton

strategies = strategies,针对每个实体对象的底层访问对像的字典strategies

connector = connector,

strategy = strategy,

errors = errors,

infos = connector:infos(),

kong_config = kong_config,

}

do

-- load DAOs

for _, schema in pairs(schemas) do

local strategy = strategies[schema.name]

if not strategy then

return nil, fmt("no strategy found for schema '%s'", schema.name)

end

      //DB中定义了daos的数据访问的抽象层字典，每个DAO封装了针对特定实体的底层数据访问对象strategy

daos[schema.name] = DAO.new(self, schema, strategy, errors)

     

end

end

-- we are 200 OK

return setmetatable(self, DB)

end

db.plugins---当找不到时，就访问元表————index,方法内转发到self.daos[plugins] //新增插件时，在初始加载插件的时，会加载插件下的daos.lua文件，构建新的dao对象，添加到db的dao字典中

注意schema定义中dao,扩展dao的访问方法（dao:new方法中会读取这个dao属性,并加载扩展当前dao对象）