### Apache Airflow version

Other Airflow 2 version (please specify below)

### What happened

Airflow 2.3.4 (but actual code seems to have same behaviour).

I have mapped task with xcom value.

I want to get xcom value of particular instance or xcom values of all task instances.

I am using standard REST API method /dags/{dag_id}/dagRuns/{dag_run_id}/taskInstances/{task_id}/xcomEntries/{xcom_key}

And it throws an error
`
  File &#34;/home/airflow/.local/lib/python3.9/site-packages/sqlalchemy/orm/query.py&#34;, line 2850, in one_or_none
    return self._iter().one_or_none()
  File &#34;/home/airflow/.local/lib/python3.9/site-packages/sqlalchemy/engine/result.py&#34;, line 1510, in one_or_none
    return self._only_one_row(
  File &#34;/home/airflow/.local/lib/python3.9/site-packages/sqlalchemy/engine/result.py&#34;, line 614, in _only_one_row
    raise exc.MultipleResultsFound(
sqlalchemy.exc.MultipleResultsFound: Multiple rows were found when one or none was required
`

Is it any way of getting xcom of mapped tasks via API?

### What you think should happen instead

_No response_

### How to reproduce

Make dag with mapped task. Return xcom value in every task. Try to get xcom value via API.

### Operating System

ubuntu 20.04

### Versions of Apache Airflow Providers

_No response_

### Deployment

Other

### Deployment details

Standard

### Anything else

_No response_

### Are you willing to submit PR?

- [ ] Yes I am willing to submit a PR!

### Code of Conduct

- [X] I agree to follow this project's [Code of Conduct](https://github.com/apache/airflow/blob/main/CODE_OF_CONDUCT.md)

#
#
from __future__ import annotations
import json
import os
import subprocess
import sys
from contextlib import ExitStack, suppress
from datetime import datetime, timedelta
from typing import TYPE_CHECKING
import pytest
import time_machine
from itsdangerous import URLSafeSerializer
assert "airflow" not in sys.modules, "No airflow module can be imported before these lines"
tests_directory = os.path.dirname(os.path.realpath(__file__))
os.environ["AIRFLOW__CORE__DAGS_FOLDER"] = os.path.join(tests_directory, "dags")
os.environ["AIRFLOW__CORE__UNIT_TEST_MODE"] = "True"
os.environ["AWS_DEFAULT_REGION"] = os.environ.get("AWS_DEFAULT_REGION") or "us-east-1"
os.environ["CREDENTIALS_DIR"] = os.environ.get("CREDENTIALS_DIR") or "/files/airflow-breeze-config/keys"
os.environ["AIRFLOW_ENABLE_AIP_44"] = os.environ.get("AIRFLOW_ENABLE_AIP_44") or "true"
from airflow import settings  
from airflow.models.tasklog import LogTemplate  
from tests.test_utils.db import clear_all  
from tests.test_utils.perf.perf_kit.sqlalchemy import (  
    count_queries,
    trace_queries,
)
if TYPE_CHECKING:
    from airflow.models.taskinstance import TaskInstance