Add support for sqlalchemy.dialects.postgresql fields

When I try to register a SQLAlchemyNode whose model has a postgres-specific field, I receive the error message Don't know how to convert the SQLAlchemy field [table_name].[field_name] (<class 'sqlalchemy.sql.schema.Column'>). It’d be great if these fields worked out of the box.

[patvdleer]

Due a wrapper (for JSONB on Sqlite) I wrote (and stole/copied) I ran into the same error. Maybe this will help others.

import json

from graphene import JSONString
from graphene_sqlalchemy.converter import convert_sqlalchemy_type, get_column_doc, is_column_nullable
from sqlalchemy import types, TypeDecorator
from sqlalchemy.dialects.postgresql import JSONB
from sqlalchemy.ext.compiler import compiles
from sqlalchemy.sql import sqltypes
from sqlalchemy.sql.functions import FunctionElement


class SqliteJsonElement(FunctionElement):
    type = types.Text()
    name = "JsonElement"

    @property
    def astext(self):
        return self


@compiles(SqliteJsonElement)
def compileSqliteJsonElement(element, compiler, **kw):
    return "jsonExtract(%s)" % compiler.process(element.clauses)


class SqliteJson(TypeDecorator):
    impl = types.Text

    def process_bind_param(self, value, dialect):
        if isinstance(value, tuple) and len(value) == 1:
            value = value[0]
        return json.dumps(value or {})

    def process_result_value(self, value, dialect):
        if value is None:
            return {}
        return json.loads(value)

    class comparator_factory(sqltypes.Concatenable.Comparator):
        def __getitem__(self, other):
            """Get the value at a given key."""
            return SqliteJsonElement(self.expr, other)


class SqliteCompatiblePostgresOptimizedJson(TypeDecorator):
    # See: http://docs.sqlalchemy.org/en/latest/core/custom_types.html
    # impl = None
    impl = types.JSON

    def load_dialect_impl(self, dialect):
        dialectTypeMap = {
            'sqlite': SqliteJson,
            'postgresql': JSONB
        }

        self.impl = dialect.type_descriptor(dialectTypeMap[dialect.name])
        return self.impl

    def process_bind_param(self, value, dialect):
        return value

    def process_result_value(self, value, dialect):
        # Todo: refactor
        if isinstance(value, (tuple, list)) and len(value) == 1:
            value = value[0]
        if isinstance(value, dict) and len(value.keys()) == 1 and "meta" in value.keys():
            value = value["meta"]
        return value

    @property
    def comparator_factory(self):
        """express comparison behavior in terms of the base type"""
        return self.impl.comparator_factory


@convert_sqlalchemy_type.register(SqliteCompatiblePostgresOptimizedJson)
def convert_json_to_string(type, column, registry=None):
    return JSONString(description=get_column_doc(column), required=not(is_column_nullable(column)))

[syrusakbary]

Postgresql SQLAlchemy field conversion is now available in 1.0.dev (master branch).

Closing the issue!