Azure Logic App - Add to existing ArrayList in a Object

I am trying to create a LogicApp which can add to an existing object. I initialized two variables in the below details.

Object1
{
  "Email": "[email protected]",
  "FirstName": "test",
  "LastName": "tester",
  "Memberships": [
    {
      "id": "1"
    },
    {
      "id": "2"
    }
  ]
}

Object2
{
  "Memberships": [
    {
      "id": "3"
    }
  ]
}

FinalResult
{
  "Email": "[email protected]",
  "FirstName": "test",
  "LastName": "tester",
  "Memberships": [
    {
      "id": "1"
    },
    {
      "id": "2"
    },
    {
      "id": "3"
    }
  ]
}

Using a Compose Component I tried union(variable(object1),variable(object2)) and this did not add Membership ID 3.

Any help is appreciated.

Solution

I have reproduced in my environment and got expected results as below:

Design:

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clearly:

union(variables('var1')['Memberships'],variables('var2')['Memberships'])

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Output:

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Codeview:

{
    "definition": {
        "$schema": "https://schema.management.azure.com/providers/Microsoft.Logic/schemas/2016-06-01/workflowdefinition.json#",
        "actions": {
            "Compose": {
                "inputs": "@union(variables('var1')['Memberships'],variables('var2')['Memberships'])",
                "runAfter": {
                    "Parse_JSON_2": [
                        "Succeeded"
                    ]
                },
                "type": "Compose"
            },
            "Initialize_variable": {
                "inputs": {
                    "variables": [
                        {
                            "name": "var1",
                            "type": "object",
                            "value": {
                                "Email": "[email protected]",
                                "FirstName": "test",
                                "LastName": "tester",
                                "Memberships": [
                                    {
                                        "id": "1"
                                    },
                                    {
                                        "id": "2"
                                    }
                                ]
                            }
                        }
                    ]
                },
                "runAfter": {},
                "type": "InitializeVariable"
            },
            "Initialize_variable_2": {
                "inputs": {
                    "variables": [
                        {
                            "name": "var2",
                            "type": "object",
                            "value": {
                                "Memberships": [
                                    {
                                        "id": "3"
                                    }
                                ]
                            }
                        }
                    ]
                },
                "runAfter": {
                    "Parse_JSON": [
                        "Succeeded"
                    ]
                },
                "type": "InitializeVariable"
            },
            "Initialize_variable_3": {
                "inputs": {
                    "variables": [
                        {
                            "name": "var3",
                            "type": "object",
                            "value": {
                                "Email": "@body('Parse_JSON')?['Email']",
                                "FirstName": "@body('Parse_JSON')?['FirstName']",
                                "LatsName": "@body('Parse_JSON')?['LastName']",
                                "Memberships": "@outputs('Compose')"
                            }
                        }
                    ]
                },
                "runAfter": {
                    "Compose": [
                        "Succeeded"
                    ]
                },
                "type": "InitializeVariable"
            },
            "Parse_JSON": {
                "inputs": {
                    "content": "@variables('var1')",
                    "schema": {
                        "properties": {
                            "Email": {
                                "type": "string"
                            },
                            "FirstName": {
                                "type": "string"
                            },
                            "LastName": {
                                "type": "string"
                            },
                            "Memberships": {
                                "items": {
                                    "properties": {
                                        "id": {
                                            "type": "string"
                                        }
                                    },
                                    "required": [
                                        "id"
                                    ],
                                    "type": "object"
                                },
                                "type": "array"
                            }
                        },
                        "type": "object"
                    }
                },
                "runAfter": {
                    "Initialize_variable": [
                        "Succeeded"
                    ]
                },
                "type": "ParseJson"
            },
            "Parse_JSON_2": {
                "inputs": {
                    "content": "@variables('var2')",
                    "schema": {
                        "properties": {
                            "Memberships": {
                                "items": {
                                    "properties": {
                                        "id": {
                                            "type": "string"
                                        }
                                    },
                                    "required": [
                                        "id"
                                    ],
                                    "type": "object"
                                },
                                "type": "array"
                            }
                        },
                        "type": "object"
                    }
                },
                "runAfter": {
                    "Initialize_variable_2": [
                        "Succeeded"
                    ]
                },
                "type": "ParseJson"
            }
        },
        "contentVersion": "1.0.0.0",
        "outputs": {},
        "parameters": {},
        "triggers": {
            "manual": {
                "inputs": {
                    "schema": {}
                },
                "kind": "Http",
                "type": "Request"
            }
        }
    },
    "parameters": {}
}