How to write my own dialect in sqlalchemy to adapt HTTP API?

问题

I'm trying to add a special data source to Superset (a data exploration platform). This database only supports HTTP API, and returns data in json format. ex:

> http://localhost/api/sql/query?q="select * from table"
< [{"id": 1, "value":10}, {"id": 2, "value": 30} ...]

Therefore, I have to write my own adapter in python SQLAlchemy for Superset. I have read the document and part of source code, but still need good example to follow.

Could you give me some clue? Anything help is welcome.

====

UPDATE:

I have solved this problem. Here is what I do.

Go to ./site-packages/sqlalchemy/dialects
Copy any concrete dialects to the new one (eg: named zeta) as the start point. A better way is to use
```
from sqlalchemy.engine.default import DefaultDialect
class ZetaDialect(DefaultDialect):
    ...
```
Add zeta into __all__ section of ./site-packages/sqlalchemy/dialects/__init__.py

Create a test program:

from sqlalchemy import create_engine
engine = create_engine('zeta://XXX')
result = engine.execute("select * from table_name")
for row in result:
    print(row)

Run it and get error. Use pdb to find the reason. In most cases, the reason is NotImplement some interfaces. Solve it one by one.

When test program gives correct answer, it has almost been done 90%. For completeness, we should also implement several interface used by inspectors:

class ZetaDialect(DefaultDialect):
    # default_paramstyle = 'qmark'
    name = 'zeta'

    def __init__(self, **kwargs):
        DefaultDialect.__init__(self, **kwargs)

    @classmethod
    def dbapi(cls):
        return zeta_dbapi

    @reflection.cache
    def get_table_names(self, connection, schema=None, **kw):
        return [u'table_1', u'table_2', ...]

    @reflection.cache
    def get_pk_constraint(self, connection, table_name, schema=None, **kw):
        return []

    @reflection.cache
    def get_foreign_keys(self, connection, table_name, schema=None, **kw):
        return []

    @reflection.cache
    def get_unique_constraints(self, connection, table_name,
                               schema=None, **kw):
        return []

    @reflection.cache
    def get_indexes(self, connection, table_name, schema=None, **kw):
        return []

    @reflection.cache
    def get_schema_names(self, connection, **kw):
        return []

    @reflection.cache
    def get_columns(self, connection, table_name, schema=None, **kw):
        # just an example of the column structure
        result = connection.execute('select * from %s limit 1' % table_name)
        return [{'default': None, 'autoincrement': False, 'type': TEXT, 'name': colname, 'nullable': False} for colname, coltype in result.curs

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来源：https://stackoverflow.com/questions/43929132/how-to-write-my-own-dialect-in-sqlalchemy-to-adapt-http-api

标签

sqlalchemy

dialect