  A new class of models of stellar discs is introduced and used to build a
self-consistent model of our Galaxy. The model is defined by the parameters
that specify the action-based distribution functions (DFs) f(J) of four stellar
discs (three thin-disc age cohorts and a thick disc), spheroidal bulge and
spheroidal stellar and dark haloes. From these DFs plus a specified
distribution of gas, we solve for the densities of stars and dark matter and
the potential they generate. The principal observational constraints are the
kinematics of stars with Gaia RVS data and the density of stars in the column
above the Sun. The model predicts the density and kinematics of stars and dark
matter throughout the Galaxy. We determine the structure of the dark halo prior
to the infall of baryons. A simple extension of the DFs of stellar components
to include chemistry allows the model to reproduce the way the Galaxy's
chemistry is observed to vary in the (R,z) plane. Surprisingly, the data
indicate that high-alpha stars are confined to orbits with J_z >~ 50 kpc km/s.
The code used to create the model is available on Github.
