docs/exampleusage.md
# Example Usage
## The API
The Pacifica Metadata Services API covers the complete object life-cycle:
create, read, update, and delete.
The examples in this section demonstrate the life-cycle of the `User` object
using a Pacifica Metadata Services deployment at http://localhost:8121/ (see
"Installing the Service" section).
### Creating an Object
To create a new `User` object, start by generating a new file `create.json` to
store the JSON data:
```
{
"_id": 127,
"email_address": "john@doe.com",
"first_name": "John",
"last_name": "Doe",
"middle_initial": "",
"network_id": "guest"
}
```
Then, provide the contents of the new file as the body for a HTTP PUT request
using the `curl` command:
```sh
curl -X PUT -T create.json 'http://localhost:8121/users'
```
### Reading an Object
To retrieve the JSON data for the `User` object that was just created, send a
HTTP GET request (with the `_id` attribute as a query parameter) using the
`curl` command:
```sh
curl -X GET 'http://localhost:8121/users?_id=127'
```
The response body is a JSON array of JSON objects.
Because the query uses the `_id` attribute, a primary key, the JSON array
contains either zero (no match) or one (match) JSON objects:
```
[
{
"_id": 127,
"email_address": "john@doe.com",
"encoding": "UTF8",
"first_name": "John",
"last_name": "Doe",
"middle_initial": "",
"network_id": "guest",
"created": 1459204793,
"deleted": null,
"updated": 1459204793
}
]
```
Optionally, query on any other parts of an object by using its attributes as
query parameters, e.g., to query on both the `first_name` and `last_name`
attributes using the `curl` command:
```
curl -X GET 'http://localhost:8121/users?last_name=Doe&first_name=John'
```
Response bodies for queries on other parts may contain JSON data for more than
one match:
```
[
{
"_id": 127,
"email_address": "john@doe.com",
"encoding": "UTF8",
"first_name": "John",
"last_name": "Doe",
"middle_initial": "",
"network_id": "guest",
"created": 1459204793,
"deleted": null,
"updated": 1459204793
},
...
]
```
#### Pagination
By default, Pacifica Metadata Services API endpoints respond with JSON data for
all matching objects.
Hence, the response size, and therefore, the response time is proportional to
the number of matches.
To reduce the response time, but still enable access to all matching objects,
all Pacifica Metadata Services API endpoints offer a "pagination" capability,
where large responses are subdivided into "pages" with a fixed number of
matching objects "per page".
For example, 100 matching objects are divided into 4 pages of 25 matching
objects per page:
* Page 1 = Matching objects 1 to 25
* Page 2 = Matching objects 26 to 50
* Page 3 = Matching objects 51 to 75
* Page 4 = Matching objects 76 to 100
* Page >4 = No matching objects
Use the `page_number` and `items_per_page` query parameters to specify the
number of pages and the number of matching objects per page, respectively, e.g.,
to retrieve the 7th page of 10 `User`s per page using the `curl` command:
```
curl -X GET 'http://localhost:8121/users?items_per_page=10&page_number=7'
```
### Updating an Object
To modify a preexisting object, use the query parameters to identify the object
(or objects) and then send a HTTP POST request with the JSON data for the
modified attributes as the request body, e.g., to modify the `network_id`
attribute, start by generating a new file `update.json` to store the JSON data:
```
{
"network_id": "example"
}
```
Then, provide the contents of the new file as the body for a HTTP POST request
using the `curl` command:
```sh
curl -X POST -T update.json 'http://localhost:8121/users?last_name=Doe&first_name=John'
```
Finally, verify the modifications by retrieving the most recent version of the
object (see "Reading an Object" section), e.g., using the `curl` command:
```sh
curl -X GET 'http://localhost:8121/users?_id=127'
```
The `updated` attribute is automatically set to the current time when an object
is modified:
```
[
{
"_id": 127,
"email_address": "john@doe.com",
"encoding": "UTF8",
"first_name": "John",
"last_name": "Doe",
"middle_initial": "",
"network_id": "example",
"created": 1459204793,
"deleted": null,
"updated": 1459205143
}
]
```
### (Soft) Deleting an Object
To mark an object as `deleted`, i.e., to "soft delete" an object, send a HTTP
DELETE request using the `curl` command:
```sh
curl -X DELETE 'http://localhost:8121/users?_id=127'
```
**NOTE** Don't worry! The object isn't really deleted.
Finally, verify the "soft delete" by retrieving the most recent version of the
object (see "Reading an Object" section), e.g., using the `curl` command:
```sh
curl -X GET 'http://localhost:8121/users?_id=127'
```
The `deleted` attribute is automatically set to the current time when an object
is "soft deleted":
```
[
{
"_id": 127,
"email_address": "john@doe.com",
"encoding": "UTF8",
"first_name": "John",
"last_name": "Doe",
"middle_initial": "",
"network_id": "example",
"created": 1459204793,
"deleted": 1459205341,
"updated": 1459205143
}
]
```