Merge 78f6960 into 798258d

src/JuMP.jl

@@ -549,21 +549,58 @@ function dual(cr::ConstraintRef{Model, <:MOICON})
                    dual_shape(cr.shape))
 end
 
+"""
+    struct OptimizeNotCalled <: Exception end
+
+A result attribute cannot be queried before [`optimize!`](@ref) is called.
+"""
+struct OptimizeNotCalled <: Exception end
+
+# Throws an error if `optimize!` has not been called, i.e., if there is no
+# optimizer attached or if the termination statis is `MOI.OPTIMIZE_NOT_CALLED`.
+function moi_get_result(model::MOI.ModelLike, args...)
+    if MOI.get(model, MOI.TerminationStatus()) == MOI.OPTIMIZE_NOT_CALLED
+        throw(OptimizeNotCalled())
+    end
+    return MOI.get(model, args...)
+end
+function moi_get_result(model::MOIU.CachingOptimizer, args...)
+    if MOIU.state(model) == MOIU.NO_OPTIMIZER ||
+       MOI.get(model, MOI.TerminationStatus()) == MOI.OPTIMIZE_NOT_CALLED
+        throw(OptimizeNotCalled())
+    end
+    return MOI.get(model, args...)
+end
+
 """
     get(m::JuMP.Model, attr::MathOptInterface.AbstractModelAttribute)
 
 Return the value of the attribute `attr` from model's MOI backend.
 """
-MOI.get(m::Model, attr::MOI.AbstractModelAttribute) = MOI.get(backend(m), attr)
+function MOI.get(model::Model, attr::MOI.AbstractModelAttribute)
+    if MOI.is_set_by_optimize(attr)
+        moi_get_result(backend(model), attr)
+    else
+        MOI.get(backend(model), attr)
+    end
+end
 function MOI.get(model::Model, attr::MOI.AbstractVariableAttribute,
                  v::VariableRef)
     check_belongs_to_model(v, model)
-    return MOI.get(backend(model), attr, index(v))
+    if MOI.is_set_by_optimize(attr)
+        return moi_get_result(backend(model), attr, index(v))
+    else
+        return MOI.get(backend(model), attr, index(v))
+    end
 end
 function MOI.get(model::Model, attr::MOI.AbstractConstraintAttribute,
                  cr::ConstraintRef)
     check_belongs_to_model(cr, model)
-    return MOI.get(backend(model), attr, index(cr))
+    if MOI.is_set_by_optimize(attr)
+        return moi_get_result(backend(model), attr, index(cr))
+    else
+        return MOI.get(backend(model), attr, index(cr))
+    end
 end
 
 MOI.set(m::Model, attr::MOI.AbstractModelAttribute, value) = MOI.set(backend(m), attr, value)

test/model.jl

@@ -42,6 +42,19 @@ end
 include("nonnegative_bridge.jl")
 
 function test_model()
+    @testset "Result attributes" begin
+        err = JuMP.OptimizeNotCalled()
+        model = Model()
+        @variable(model, x)
+        c = @constraint(model, x ≤ 0)
+        @objective(model, Max, x)
+        @test_throws err JuMP.objective_value(model)
+        @test_throws err JuMP.objective_bound(model)
+        @test_throws err JuMP.value(x)
+        @test_throws err JuMP.value(c)
+        @test_throws err JuMP.dual(c)
+    end
+
     @testset "Test variable/model 'hygiene'" begin
         model_x = Model()
         @variable(model_x, x)