dbrequests 1.4.8
Python package for querying and connecting to databases.
License: MIT

# dbrequests

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**dbrequests is a python package built for easy use of raw SQL within python and pandas projects.**

It uses ideas from [records](https://github.com/kennethreitz/records/) and is built using [sqlalchemy-engines](https://www.sqlalchemy.org/), but is more heavily integrated with pandas. It aims to reproduce the pilosophy behind the R-package [dbtools](https://github.com/INWT/dbtools/).


_Database support includes RedShift, Postgres, MySQL, SQLite, Oracle, and MS-SQL (drivers not included)._

## Usage

### Send queries and bulk queries

Easy sending of raw sql and output as pandas DataFrames, with credentials given as dictionary (for an example see creds_example.json) or the url of the database:

```python
from dbrequests import Database

db = Database(creds=creds)
df = db.send_query("""
    SELECT * FROM test;
    """)
df # table test as pandas DataFrame
```

You can put the sql query in a file and direct `send_query` to the file. The sql-file may be parametrized:

```sql
SELECT {col1}, {col2} FROM test;

```

```python
from dbrequests import Database

db = Database(creds=creds, sql_dir = '/path/to/dir/')
db.send_query('select', col1='id', col2='name')
df # table test, including columns 'id', 'name' as pandas DataFrame
```

You can also pass arguments to pandas `read_sql`-Function:

```python
from dbrequests import Database

db = Database(creds=creds, sql_dir = '/path/to/dir/')
db.send_query('select', col1='id', col2='name', index_col='id')
df # table test, including column 'name' as pandas DataFrame with index 'id'
```

You may also send queries with no table as output to the database via `send_bulk_query`, which exhibits the same behavior as `send_query`:

```python
db.send_bulk_query('drop test from test;')
```

### Send data

Easy sending of pandas Dataframes in multiple modes:

```python
db.send_data(df, 'table', mode='insert')
```

Supported modes are:
  - 'insert': Appending new records. Duplicate primary keys will result in errors (sql insert into).
  - 'truncate': Delete the table and completely rewrite it (sql truncate and insert into).
  - 'replace': Replace records with duplicate primary keys (sql replace into).
  - 'update': Update records with duplicate primary keys (sql insert into duplicate key update).

### Utilities

- Comments can be automatically removed from SQL code by adding `remove_comments=True` either to the Database defintion or send_query. This is especially useful if outcommenting code blocks including parametized variables and thus `{}`. The default of this behavior is `False`.
- Percentage signs can be transfered to a Python readable way by adding `escape_percentage=True` either to the Database definition or send_query. This means percentage signs dont have to be escaped manually when sending them via Python. The default is `False`.
- Database.get_table_names will give existing tables in the database
- Parameters such es `chunksize` for `pandas.to_sql` may be given to the wrapper function `send_data` and are handed over to pandas. The same is true for `send_query`.
- For transactions the context manager `transaction` may be of use.

## Installation

The package can be installed via pip:

```
pip install dbrequests
```

## Extensibility
dbrequests is designed to easily accommodate different needs in the form of drivers / dialects. For examples of how to extend the capabilities of the Connection class, see connection_subclass.py under examples.

### Existing extensions
- MySQL / MariaDB: use
```
from dbrequests.mysql import Database
```
for using the MySQL specific extension as Database connector. The extension provides MySQL specific functionalities, like using `load data infile` for writing data to tables.


## Version 1.0
  - implemented send_data and send_query wrappers for pandas sql-functionality

## Version 1.0.8
  - renamed to dbrequests

## Version 1.1
  - added handling of percentage signs
  - added possibility of automated comment removal
  - ensured the compatibility of raw SQL code with code sent via dbrequests

## Version 1.2
  -  changed static loading of the connection class to a flexible model, allowing to override connections for different SQL drivers

## Version 1.3
  - added mysql backend for specific mysql and mariadb support
  - added possibility for send_data to use infile for mysql databases

## Version 1.3.8
  - dbrequests.mysql module:
    - see #11 for motivation on moving dialect specific implementation into extras
    - see #15 for mysql specific send_data via load data local infile

## Version 1.3.9
  - dbrequests.mysql:
    - see #20 for memory efficient send_data using datatable

## Version 1.3.10
  - dbrequests.mysql:
    - see #24 for bugfix while writing to csv

## Version 1.3.11
  - dbrequests.mysql:
    - see #28 for bugfix when sending escape sequences

## Version 1.3.12
  - dbrequests.mysql:
    - see #22 for performance improvements for send_query when reading large datasets
    - support for pymysql and mysqldb

## Version 1.3.13
  - dbrequests.mysql
    - see #30: fixes handling of None/NULL values in columns

## Version 1.3.14
  - dbrequests.mysql:
    - see #32 for bugfix in send_query for empty result sets

## Version 1.3.15
  - dbrequests:
    - see #27 for bugfix in Database class when specifiying a port in a
      credentials object.
    - the argument 'creds' in the init method of a database class is now
      deprecated
    - the argument 'db_url' can now handle str and dict type; str is a
      sqlalchemy url; a dict a credentials object
    - credential objects can now have additional fields which will be used as
      elements in connect_args for sqlalchemies create_engine: see #12
  - dbrequests.mysql
    - see #36 for bugfix while sending an empty frame

## Version 1.3.16
  - dbrequests.mysql
    - see #35: New send_data modes: update_diffs, insert_diffs, replace_diffs

## Version 1.3.17
  - dbrequests.mysql
    - new function in database: send_delete for deleting rows in a database.
    - send_data in mode 'update' now allows to send only partial subset of
      columns.

## Version 1.4.0
  - dbrequests.mysql
    - bugfix in send_data with mode [update|insert|replace]_diffs: same as #36

## Version 1.4.1
  - dbrequests.mysql
    - bugfix for upstream bug in mariadb: sending diffs needs persisten tables
      instead of temporary.

## Version 1.4.2
  - dbrequests.mysql
    - creating temorary removing partitions and system versioned from temporary
      tables.
    - new mode for send data: sync_diffs: update differences and delete
      deprecated rows.
    - new mode for delete data: in_delete_col: mark rows to delete, then delete.
    - bugfix for temporary tables: now properly removes tables.

## Version 1.4.3-5
  - dbrequests.mysql
    - More stable and reliable Version of sync_diffs mode for sending data.
      Respects scarce resources on the mysql server.

## Version 1.4.6
  - dbrequests.mysql
    - HOTFIX #51: Bug with latest datatable version

## Version 1.4.7
  - dbrequests.mysql
    - bugfix of #52

## Version 1.4.8
  - dbrequests.mysql
    - fix for creating temporary files on Windows.