<h2>简单的实现</h2>
<p>你可以用这样的东西:</p>
<pre><code>from sqlalchemy.ext.declarative import DeclarativeMeta
class AlchemyEncoder(json.JSONEncoder):
def default(self, obj):
if isinstance(obj.__class__, DeclarativeMeta):
# an SQLAlchemy class
fields = {}
for field in [x for x in dir(obj) if not x.startswith('_') and x != 'metadata']:
data = obj.__getattribute__(field)
try:
json.dumps(data) # this will fail on non-encodable values, like other classes
fields[field] = data
except TypeError:
fields[field] = None
# a json-encodable dict
return fields
return json.JSONEncoder.default(self, obj)
</code></pre>
<p>然后使用以下命令转换为JSON:</p>
<pre><code>c = YourAlchemyClass()
print json.dumps(c, cls=AlchemyEncoder)
</code></pre>
<p>它将忽略不可编码的字段(将它们设置为“无”)。</p>
<p>它不会自动扩展关系(因为这可能导致自引用,并永远循环)。</p>
<h2>递归的、非循环的实现</h2>
<p>但是,如果您希望永远循环,您可以使用:</p>
<pre><code>from sqlalchemy.ext.declarative import DeclarativeMeta
def new_alchemy_encoder():
_visited_objs = []
class AlchemyEncoder(json.JSONEncoder):
def default(self, obj):
if isinstance(obj.__class__, DeclarativeMeta):
# don't re-visit self
if obj in _visited_objs:
return None
_visited_objs.append(obj)
# an SQLAlchemy class
fields = {}
for field in [x for x in dir(obj) if not x.startswith('_') and x != 'metadata']:
fields[field] = obj.__getattribute__(field)
# a json-encodable dict
return fields
return json.JSONEncoder.default(self, obj)
return AlchemyEncoder
</code></pre>
<p>然后使用以下方法对对象进行编码:</p>
<pre><code>print json.dumps(e, cls=new_alchemy_encoder(), check_circular=False)
</code></pre>
<p>这将编码所有的孩子,所有的孩子,所有的孩子。。。基本上可以对整个数据库进行编码。当它到达之前编码的东西时,它会将其编码为“无”。</p>
<h2>递归的,可能是循环的,选择性的实现</h2>
<p>另一个可能更好的选择是能够指定要展开的字段:</p>
<pre><code>def new_alchemy_encoder(revisit_self = False, fields_to_expand = []):
_visited_objs = []
class AlchemyEncoder(json.JSONEncoder):
def default(self, obj):
if isinstance(obj.__class__, DeclarativeMeta):
# don't re-visit self
if revisit_self:
if obj in _visited_objs:
return None
_visited_objs.append(obj)
# go through each field in this SQLalchemy class
fields = {}
for field in [x for x in dir(obj) if not x.startswith('_') and x != 'metadata']:
val = obj.__getattribute__(field)
# is this field another SQLalchemy object, or a list of SQLalchemy objects?
if isinstance(val.__class__, DeclarativeMeta) or (isinstance(val, list) and len(val) > 0 and isinstance(val[0].__class__, DeclarativeMeta)):
# unless we're expanding this field, stop here
if field not in fields_to_expand:
# not expanding this field: set it to None and continue
fields[field] = None
continue
fields[field] = val
# a json-encodable dict
return fields
return json.JSONEncoder.default(self, obj)
return AlchemyEncoder
</code></pre>
<p>您现在可以用以下方法调用它:</p>
<pre><code>print json.dumps(e, cls=new_alchemy_encoder(False, ['parents']), check_circular=False)
</code></pre>
<p>例如,只扩展名为“parents”的SQLAlchemy字段。</p>