Break upsert() into component parts

[goatchurchprime]

Function is here:
https://github.com/okfn/webstore/blob/master/webstore/views.py#L203

In scraperwiki this is the save(unique_keys=[], data={}) function.

It makes the following distinct processes:

1. create table if not exists
2. add columns to existing table [ done with _ensure_columns ]
3. create an index table for unique_keys [ method from scraperwiki, not webstore ]
4. update_row (or insert row) of the table

Unique keys are fetched from query_string by request.args.getlist('unique')

The scraperwiki version has an extra jargtypes={key:type} to define the types of the columns and avoid the derivation of variable types happening at the wrong side of the json interface.

Option 1:

Combine steps 1,2,3 into one table schema updating function, and then 4 can be a normal sql update function

Option 2:

Get the client to fetch the schema from webstore at the start and then perform all the computation go generate the schema updates there

[goatchurchprime]

The current upsert function allows bulk uploading of records from a csv file directly.

Proposal is to keep this function but rewrite it to expose two further functions in the interface:

1. a schema update function, which is like making the following function writable
   GET /{user-name}/{db-name}/{table-name}/schema

This is not the same as exposing the "CREATE TABLE IF NOT EXISTS" function because that function does not alter tables. It would provide a route towards extra altering functions, such as dropping columns or changing their type -- features which are not given by the underlying database.

This function takes the jargtypes thing as it stands.

2. An upsert() function taking a list of data rows (filling in missing elements with nulls).

[Discussion to follow of whether unique_keys information is part of the schema, or part of the upsert function.]