django-pgjsonb 0.0.20

Django Postgres JSONB Fields support with lookups

# django-pgjsonb
Django Postgres JSONB Fields support with lookups

Originaly inspired by [django-postgres](https://bitbucket.org/schinckel/django-postgres/)

Change Logs
===========
2016-03-09: 0.0.20
Add the array length for select_json
2016-03-08: 0.0.19
fix when add a json field with db_index=True and it's fail to generate the create index sql
2016-03-01: 0.0.18
we want to be able to use customize decoder to load json, so get avoid the psycopg2's decode json, just return raw text then we deserilize by the field from_db_value

2016-03-01: 0.0.17
patch the django serilizer to not return the stringifyed result

2015-07-23: 0.0.16
Add support for ./manage.py inspectdb

2015-06-10: 0.0.15
Add support for db_index to add GIN index

Install
=======

`pip install django-pgjsonb`

Definition
===

```python
from django_pgjsonb import JSONField

class Article(models.Model):
meta=JSONField([null=True,default={}])
```

Add Index
=====
[new add in 0.0.15]

jsonb field support gin type index to accelerator filtering. Since JSON is a data structure contains hierarchy, so the index of jsonb field will be more complicate than another single value field. More information, please referance [Postgres document 8.14.4](http://www.postgresql.org/docs/9.4/static/datatype-json.html)

```python
meta=JSONField(db_index=True)
or
meta=JSONField(db_index=True,db_index_options={"path":"authors__name","only_contains":True})
or
meta=JSONField(db_index=True,db_index_options=[{},{"path":"authors__name","only_contains":True}])
```

When set db_index as True and do not set db_index_options, it will generate default GIN index, most case it's enough.

When specify ```db_index_options={"only_contains":True}```,the index will be as the non-default GIN operator class jsonb_path_ops that supports indexing the ```contains``` operator only, but it's consume less space and more efficient.

When specify the path parameter in db_index_options, ```db_index_options={"path":"authors__name"}```, then index will generate to the specify path, so that ```Article.objects.filter(meta__authors__name__contains=["asd"])``` can utilize the index.

So you can create multiple index in one JSONField, just pass the db_index_options parameter as a list that contains multiple options, it will generate multiple correspond indexes. Empty dict stand for the default GIN index.


Lookups
=======
###Contains wide range of lookups support natively by postgres

1. `has` :if field has specific key *`("?")`*

```python
Artile.objects.filter(meta__has="author")
```

2. `has_any` : if field has any of the specific keys *`("?|")`*

```python
Artile.objects.filter(meta__has_any=["author","date"])
```
3. `has_all` : if field has all of the specific keys *`("?&")`*

```python
Artile.objects.filter(meta__has_all=["author","date"])
```
4. `contains` : if field contains the specific keys and values *`("@>")`*
```python
Article.objects.filter(meta__contains={"author":"yjmade","date":"2014-12-13"})
```

5. `in` or `contained_by` : if all field key and value contain by input *`("<@")`*
```python
Artile.objects.filter(meta__in={"author":"yjmade","date":"2014-12-13"})
```

6. `len` : the length of the array ,transform to int,and can followed int lookup like gt or lt *`("jsonb_array_length()")`*

```python
Artile.objects.filter(meta__authors__len__gte=3)
Article.objects.filter(meta__authors__len=10)
```
7. `as_(text,int,float,bool,date,datetime)` : transform json field into sepcific data type so that you can follow operation of this type *`("CAST(FIELD as TYPE)")`*

```python
Article.objects.filter(meta__date__as_datetime__year__range=(2012,2015))
Article.objects.filter(meta__view_count__as_float__gt=100)
Article.objects.filter(meta__title__as_text__iregex=r"^\d{4}")
```
8. `path_(PATH)` : get the specific path, path split by '_' *`("#>")`*

```python
Article.objects.filter(meta__path_author_articles__contains="show me the money")
```

Add function to QuerySet
========================
1.`select_json("JSON_PATHS",field_name="JSON_PATHS")`

JSON_PATHS in format of path seperate by "__",like "meta__location__geo_info". It will use queryset's `extra` method to transform a value inside json as a field.
If no fields_name provided,it will generate a field name with lookups seperate by _ without the json field self's name,so `select_json("meta__author__name")` equal to `select_json("author_name")`

```python
Article.objects.select_json("meta__author__name",geo="meta__location__geo_info")`
```

This operation will translate to sql as

```sql
SELECT "article"."meta"->'location'->'geo_info' as "geo", "article"."meta"->'author'->'name' as "author_name"
```

new add in 0.0.20
You can also select the length of a json array as a field by use Length object

```python
from django.pgjsonb.fields import Length
Article.objects.select_json(authors_len=Length("meta__authors")).values("authors_len")
```

After select_json ,the field_name can be operate in values() and values_list() method,so that

1. select only one specific value inside json
2. to group by one value inside json

is possible.

Demo:

```python
Article.objects.all().select_json(tags="meta__tags").values_list("tags")
# select only "meta"->'tags'

Article.objects.all().select_json(author_name="meta__author__name")\
.values("author_name").annotate(count=models.Count("author_name"))
# GROUP BY "meta"->'author'->'name'
```




#####For more infomation about raw jsonb operation,please see [PostgreSQL Document](http://www.postgresql.org/docs/9.4/static/functions-json.html)