Alater the Milvus meta fields manually.

N8N subflow - Alter Milvus DB Fields.json

{
  "nodes": [
    {
      "parameters": {
        "method": "POST",
        "url": "={{ $('Start').item.json.milvus_url }}/v2/vectordb/collections/fields/alter_properties",
        "sendBody": true,
        "specifyBody": "json",
        "jsonBody": "={\n  \"collectionName\": \"{{ $('Start').item.json.collection_name }}\",\n  \"fieldName\": \"{{ $json.fields }}\",\n  \"fieldParams\": { \"max_length\": \"{{ $('Set fields to adjust').item.json.field_length }}\" }\n}",
        "options": {}
      },
      "type": "n8n-nodes-base.httpRequest",
      "typeVersion": 4.2,
      "position": [
        -112,
        656
      ],
      "id": "1dfb834f-8870-4db8-95f8-799fea2028ad",
      "name": "Alter Db"
    },
    {
      "parameters": {
        "workflowInputs": {
          "values": [
            {
              "name": "milvus_url"
            },
            {
              "name": "collection_name"
            }
          ]
        }
      },
      "id": "68241ef9-3657-420c-91ec-2c9108934259",
      "typeVersion": 1.1,
      "name": "Start",
      "type": "n8n-nodes-base.executeWorkflowTrigger",
      "position": [
        -768,
        656
      ]
    },
    {
      "parameters": {
        "assignments": {
          "assignments": [
            {
              "id": "4018060a-f69d-4a2c-95d6-a83a681dd81c",
              "name": "fields",
              "value": "={{ [\"langchain_text\", \"loc\", \"title\", \"url\"] }}",
              "type": "array"
            },
            {
              "id": "04495bff-62e3-4bcd-99b8-f2464d29f83a",
              "name": "field_length",
              "value": "2048",
              "type": "string"
            }
          ]
        },
        "options": {}
      },
      "type": "n8n-nodes-base.set",
      "typeVersion": 3.4,
      "position": [
        -560,
        656
      ],
      "id": "9c837e24-924d-4f70-a649-321361387024",
      "name": "Set fields to adjust"
    },
    {
      "parameters": {
        "fieldToSplitOut": "fields",
        "options": {}
      },
      "type": "n8n-nodes-base.splitOut",
      "typeVersion": 1,
      "position": [
        -336,
        656
      ],
      "id": "7f141f70-22ea-42ae-8802-bd089f370370",
      "name": "Split Out"
    }
  ],
  "connections": {
    "Start": {
      "main": [
        [
          {
            "node": "Set fields to adjust",
            "type": "main",
            "index": 0
          }
        ]
      ]
    },
    "Set fields to adjust": {
      "main": [
        [
          {
            "node": "Split Out",
            "type": "main",
            "index": 0
          }
        ]
      ]
    },
    "Split Out": {
      "main": [
        [
          {
            "node": "Alter Db",
            "type": "main",
            "index": 0
          }
        ]
      ]
    }
  },
  "pinData": {
    "Start": [
      {
        "milvus_url": "http://localhost:19530",
        "collection_name": "my_collection"
      }
    ]
  },
  "meta": {
    "instanceId": "12aa4b47b8cf3d835676e10b2bf760a80a1ff52932c9898603f7b21fc5376f59"
  }
}