A database interface for document stores (like MongoDB) with type-safe queries. The idea is to have a database model as a type and have the compiler check the validity of the database queries.
In addition, the database model is inspired by the idea of a cellstore. The database model is conceived as list of datapoints.
type MyModel = Double $|$ ...
&&| Maybe Integer $|$ ...
&&| Map Integer Text $|$ ...At each datapoint an object of a certain type is stored (as document).
The object can be any Haskell type, given it has - in the case of
MongoDB as backend - a suitable BSON instance.
Datapoints are specified as lists of aspects and each aspect is a pair of a dimension and a list of dimensional values.
type MyModel = Double $|$ Aspect "Category" '["Monetary"]
|$ Aspect "Currency" '["EUR", "USD", "ZWL"]
&&| Maybe Integer $|$ Aspect "Category" '["Rank"]
|$ Aspect "Currency" '["EUR", "USD", "ZWL"]
&&| ...Queries for objects in the database are types that are constructed by specifying a datapoint.
type AQuery = Aspect "Category" "Monetary"
|$ Aspect "Currency" "EUR"The compiler can infer the type of the query result given a model
(Integer, in the example).
More complex queries use type-level lists for the dimensional values, resulting in lists as result type ...
type AListQuery = Aspect "Category" '["Monetary"]
|$ Aspect "Currency" '["EUR", "USD", "ZWL"]Or tuples ((Double, Maybe Integer) in the example,
no idea how implement that, yet).
type ATupleQuery = Aspect "Category" '["Monetary", "Rank"]
|$ Aspect "Currency" '["EUR"]This is work-in-progress.
See SimpleModel and test in src/Lib.hs to get an idea.
There is a stack.yaml, so
stack build
stack exec cellstore-exe