Json to list of objects with marshmellow Python

Question

I have json with data about my object I created schema for serialize it into list of objects, but it isn't work

Schema:

from marshmellow import fields, Schema

class ContactSchema(Schema):
    first_name = fields.String(attribute="ftNm")
    last_name = fields.String(attribute="ltNm")
    phone = fields.Integer(attribute="pn")

Model:

class Contact:
    id: int
    first_name: str
    last_name: str
    phone: str

And i have a function to convert (but is not working)

def json_to_list():
    json = [{'ftNm': 'Name1', 'ltNm': 'Surname1', 'pn': 343434},
            {'ftNm': 'Name2', 'ltNm': 'Surname2', 'pn': 141414}, 
            {'ftNm': 'Name3', 'ltNm': 'Surname3', 'pn': 656565}]

    schema = ContactSchema()
    result = schema.dump(json)

I will appreciate if someone help me with function to convert json to list of objects

but is not working – what's the error?

Alderven
– Alderven

2020-09-22 09:42:15 +00:00
Commented Sep 22, 2020 at 9:42 — Alderven
– Alderven, Commented Sep 22, 2020 at 9:42
there is just logic error, I just need the right function

dangost
– dangost

2020-09-22 09:47:07 +00:00
Commented Sep 22, 2020 at 9:47 — dangost
– dangost, Commented Sep 22, 2020 at 9:47

Detlef · Accepted Answer · 2020-09-22 14:44:19Z

I'm not exactly sure what your intentions are. However, serialization and deserialization are possible in the following ways.

Serialization and deserialization with renaming of the attributes specified by the variable names.

from marshmallow import Schema, fields
    
class ContactSchema(Schema):
    first_name = fields.Str(attribute="ftNm", data_key="ftNm")
    last_name = fields.Str(attribute="ltNm", data_key="ltNm")
    phone = fields.Integer(attribute="pn", data_key="pn")

# serialization to json
def from_list():
    data = [
        {'ftNm': 'Name1', 'ltNm': 'Surname1', 'pn': 343434},
        {'ftNm': 'Name2', 'ltNm': 'Surname2', 'pn': 141414},
        {'ftNm': 'Name3', 'ltNm': 'Surname3', 'pn': 656565}
    ]
    schema = ContactSchema(many=True)
    return schema.dump(data)

# deserialization from json
def to_list():
    json = [
        {'ftNm': 'Name1', 'ltNm': 'Surname1', 'pn': 343434},
        {'ftNm': 'Name2', 'ltNm': 'Surname2', 'pn': 141414},
        {'ftNm': 'Name3', 'ltNm': 'Surname3', 'pn': 656565}
    ]
    schema = ContactSchema(many=True)
    return schema.load(json)

Deserialization without renaming of the attributes specified by the variable names.

class ContactSchema(Schema):
    first_name = fields.Str(attribute="ftNm")
    last_name = fields.Str(attribute="ltNm")
    phone = fields.Integer(attribute="pn")

# deserialization from json
def to_list():
    json = [
        {'first_name': 'Name1', 'last_name': 'Surname1', 'phone': 343434},
        {'first_name': 'Name2', 'last_name': 'Surname2', 'phone': 141414},
        {'first_name': 'Name3', 'last_name': 'Surname3', 'phone': 656565}
    ]
    schema = ContactSchema(many=True)
    return schema.load(json)

The direction of the conversion may not be indicated correctly.

from marshmallow import Schema, fields, post_load
from dataclasses import dataclass

@dataclass
class Contact:
    # id: int
    first_name: str
    last_name: str
    phone: str

class ContactSchema(Schema):
    first_name = fields.Str(data_key="ftNm")
    last_name = fields.Str(data_key="ltNm")
    phone = fields.Integer(data_key="pn")

    @post_load
    def make_user(self, data, **kwargs):
        return Contact(**data)

# deserialization from json
def to_list():
    json = [
        {'ftNm': 'Name1', 'ltNm': 'Surname1', 'pn': 343434},
        {'ftNm': 'Name2', 'ltNm': 'Surname2', 'pn': 141414},
        {'ftNm': 'Name3', 'ltNm': 'Surname3', 'pn': 656565}
    ]
    schema = ContactSchema(many=True)
    return schema.load(json)

To serialize and deserialize a database model, I recommend flask-marshmallow and marshmallow-sqlalchemy.

dangost · Accepted Answer · 2020-09-23 07:04:44Z

0

I do not know is it normally, but I just created a simple function and deserialize through the loop

    def create(self, json: dict):
        key = Key()
        key.id = json.get("id")
        key.key_number = json.get("num")
        key.hash = json.get("hash")

        return key

answered Sep 23, 2020 at 7:04

dangost

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1 Comment

Detlef Over a year ago

Marschmallow has the advantage of a number of predefined fields and the possibility to validate them. See also the combination of marshmalllow and webargs. Especially as your project gets bigger it might help you. I am a friend of small, simple solutions and would be happy for you if your approach meets the expectation.

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