The value function retsults in Getting attribute MathOptInterface.VariablePrimal cannot be performed

[votroto]

After optimizing a model

using JuMP, PolyJuMP, Gurobi

m = Model(() -> PolyJuMP.QCQP.Optimizer(Gurobi.Optimizer()))

@variable m -1 <= c <= 1
@constraint m c ^ 2 == 0.5
@objective m Min c
optimize!(m)

I can get the result with this

MOI.get(unsafe_backend(m).model, MOI.VariablePrimal(), c.index)

but this

@show value(c)

throws an Error

LoadError: MathOptInterface.GetAttributeNotAllowed{MathOptInterface.VariablePrimal}: Getting attribute MathOptInterface.VariablePrimal(1) cannot be performed: PolyJuMP.QCQP.Optimizer{Float64, Gurobi.Optimizer} does not support getting the attribute MathOptInterface.VariablePrimal(1). You may want to use a `CachingOptimizer` in `AUTOMATIC` mode or you may need to call `reset_optimizer` before doing this operation if the `CachingOptimizer` is in `MANUAL` mode.

[odow]

Yeah I noticed this the other day, but I wasn't sure if this was a deliberate choice by @blegat?

[votroto]

Adding just a "fall through" get

function MOI.get(model::Optimizer, attr::MOI.AbstractVariableAttribute, vi::MOI.VariableIndex)
    return MOI.get(model.model, attr, vi)
end

would fix it. There are a few places in the QCQP code which do gets and sets on model.model, such a method would help there too.

[blegat]

I started a draft yesterday doing that with tests that I forgot to push

[odow]

Okay, want to make a PR?