Bugfix when copying the ExperiemntData object and add warning to `_…

…retrieve_data` (qiskit-community#1316)

### Summary

As said in qiskit-community#1314 , `copy` method in `Experiment Data` class will now
copy the `provider` attribute to the copied instance and warnning if
data isn't retrieved due to `provider=None` .
### Details and comments

Some details that should be in this section include:

- Why this change was necessary
This is a bug that the provider isn't copied. In addition,
`_retrive_data()` method in the `ExperimentData` class doesn;t retirive
data if provider is not provided. Added a warning so the user will know.

qiskit_experiments/framework/experiment_data.py

@@ -1071,6 +1071,13 @@ def _retrieve_data(self):
         """Retrieve job data if missing experiment data."""
         # Get job results if missing in experiment data.
         if self.provider is None:
+            # 'self._result_data' could be locked, so I check a copy of it.
+            if not self._result_data.copy():
+                # Adding warning so the user will have indication why the analysis may fail.
+                LOG.warning(
+                    "Provider for ExperimentData object doesn't exist, resulting in a failed attempt to"
+                    " retrieve data from the server; no stored result data exists"
+                )
             return
         retrieved_jobs = {}
         jobs_to_retrieve = []  # the list of all jobs to retrieve from the server
@@ -2293,6 +2300,7 @@ def copy(self, copy_results: bool = True) -> "ExperimentData":
         new_instance = ExperimentData(
             backend=self.backend,
             service=self.service,
+            provider=self.provider,
             parent_id=self.parent_id,
             job_ids=self.job_ids,
             child_data=list(self._child_data.values()),

qiskit_experiments/test/fake_backend.py

@@ -14,6 +14,7 @@
 import uuid
 from qiskit.circuit.library import Measure
 from qiskit.providers.backend import BackendV2
+from qiskit.providers.fake_provider import FakeProvider
 from qiskit.providers.options import Options
 from qiskit.transpiler import Target
 
@@ -27,8 +28,14 @@ class FakeBackend(BackendV2):
     Fake backend for test purposes only.
     """
 
-    def __init__(self, backend_name="fake_backend", num_qubits=1, max_experiments=100):
-        super().__init__(name=backend_name)
+    def __init__(
+        self,
+        provider=FakeProvider(),
+        backend_name="fake_backend",
+        num_qubits=1,
+        max_experiments=100,
+    ):
+        super().__init__(provider=provider, name=backend_name)
         self._target = Target(num_qubits=num_qubits)
         # Add a measure for each qubit so a simple measure circuit works
         self.target.add_instruction(Measure())

releasenotes/notes/bugfix_expdata_copy-2c73a21ad720858d.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    'copy' method under ExperimentData class now copies the provider. 
+  

test/database_service/test_db_experiment_data.py

@@ -14,6 +14,7 @@
 
 """Test ExperimentData."""
 from test.base import QiskitExperimentsTestCase
+from test.fake_experiment import FakeExperiment
 import os
 from unittest import mock
 import copy
@@ -46,6 +47,7 @@
     ExperimentStatus,
 )
 from qiskit_experiments.framework.matplotlib import get_non_gui_ax
+from qiskit_experiments.test.fake_backend import FakeBackend
 
 
 class TestDbExperimentData(QiskitExperimentsTestCase):
@@ -1044,14 +1046,12 @@ def test_additional_attr(self):
 
     def test_copy_metadata(self):
         """Test copy metadata."""
-        exp_data = ExperimentData(experiment_type="qiskit_test")
+        exp_data = FakeExperiment(experiment_type="qiskit_test").run(backend=FakeBackend())
         exp_data.add_data(self._get_job_result(1))
-        result = mock.MagicMock()
-        result.result_id = str(uuid.uuid4())
-        exp_data.add_analysis_results(result)
         copied = exp_data.copy(copy_results=False)
         self.assertEqual(exp_data.data(), copied.data())
         self.assertFalse(copied.analysis_results())
+        self.assertEqual(exp_data.provider, copied.provider)
 
     def test_copy_metadata_pending_job(self):
         """Test copy metadata with a pending job."""

test/fake_experiment.py

@@ -48,11 +48,16 @@ def _default_experiment_options(cls) -> Options:
         options.dummyoption = None
         return options
 
-    def __init__(self, physical_qubits=None):
+    def __init__(self, physical_qubits=None, backend=None, experiment_type=None):
         """Initialise the fake experiment."""
         if physical_qubits is None:
             physical_qubits = [0]
-        super().__init__(physical_qubits, analysis=FakeAnalysis())
+        super().__init__(
+            physical_qubits,
+            analysis=FakeAnalysis(),
+            backend=backend,
+            experiment_type=experiment_type,
+        )
 
     def circuits(self):
         """Fake circuits."""