From 2e1923fae48e055de987b78ae8aece431b38af18 Mon Sep 17 00:00:00 2001
From: Fabian <fab.hof@gmx.de>
Date: Thu, 4 Sep 2025 13:23:29 +0200
Subject: [PATCH] feat: add objective from variable

---
 doc/release_notes.rst  | 1 +
 linopy/model.py        | 5 ++++-
 test/test_objective.py | 7 +++++++
 3 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/doc/release_notes.rst b/doc/release_notes.rst
index daa65f52..d3721743 100644
--- a/doc/release_notes.rst
+++ b/doc/release_notes.rst
@@ -11,6 +11,7 @@ Version 0.5.6
 * Improved variable/expression arithmetic methods so that they correctly handle types
 * Gurobi: Pass dictionary as env argument `env={...}` through to gurobi env creation
 * Mosek: Remove explicit use of Env, use global env instead
+* Objectives can now be created from variables via `linopy.Model.add_objective`.
 
 **Breaking Changes**
 
diff --git a/linopy/model.py b/linopy/model.py
index c8024843..0255d00e 100644
--- a/linopy/model.py
+++ b/linopy/model.py
@@ -684,7 +684,8 @@ def add_constraints(
 
     def add_objective(
         self,
-        expr: LinearExpression
+        expr: Variable
+        | LinearExpression
         | QuadraticExpression
         | Sequence[tuple[ConstantLike, VariableLike]],
         overwrite: bool = False,
@@ -710,6 +711,8 @@ def add_objective(
                 "Objective already defined."
                 " Set `overwrite` to True to force overwriting."
             )
+        if isinstance(expr, Variable):
+            expr = 1 * expr
         self.objective.expression = expr
         self.objective.sense = sense
 
diff --git a/test/test_objective.py b/test/test_objective.py
index d0831d25..d869175a 100644
--- a/test/test_objective.py
+++ b/test/test_objective.py
@@ -31,6 +31,13 @@ def test_model(linear_objective: Objective, quadratic_objective: Objective) -> N
     assert isinstance(quadratic_objective.model, Model)
 
 
+def test_add_objective_from_variable() -> None:
+    m = Model()
+    v = m.add_variables(coords=[[1, 2, 3]])
+    m.add_objective(v)
+    assert isinstance(m.objective, Objective)
+
+
 def test_sense(linear_objective: Objective, quadratic_objective: Objective) -> None:
     assert linear_objective.sense == "min"
     assert quadratic_objective.sense == "max"