使用Vertex AI SDK（Gemini）时如何正确指定ResponseSchema？

错误原因 #

你遇到的Google.Protobuf.InvalidProtocolBufferException异常，核心原因是传入的ResponseSchema格式不符合要求。你当前使用的是Python风格的类型注解字符串，而Vertex AI的ResponseSchema要求的是符合OpenAPI 3.0规范的JSON结构，Protobuf解析器无法识别自定义的类型注解格式，因此抛出了无效wire type的错误。

正确实现步骤 #

1. 定义标准OpenAPI Schema JSON #

首先需要将你的list[Comp]结构转换为符合OpenAPI规范的JSON Schema，示例如下：

{
  "type": "array",
  "items": {
    "type": "object",
    "properties": {
      "rank": {"type": "integer"},
      "score": {"type": "integer"},
      "propertyId": {"type": "integer"},
      "address": {"type": "string"},
      "proximity": {"type": "string"},
      "price": {"type": "string"},
      "livingArea": {"type": "string"},
      "lotSize": {"type": "string"},
      "yearBuilt": {"type": "integer"},
      "bedrooms": {"type": "integer"},
      "bathrooms": {"type": "integer"},
      "notes": {"type": "string"}
    },
    "required": ["rank", "score", "propertyId", "address", "price", "bedrooms", "bathrooms"]
  }
}

2. 修改C#代码中的ResponseSchema解析逻辑 #

将原来的Python风格字符串替换为上述标准JSON结构，修改后的GenerationConfig部分代码如下：

GenerationConfig = new GenerationConfig
{
    CandidateCount = 1,
    Temperature = Temperature,
    MaxOutputTokens = args.MaxOutputTokens ?? MaxOutputTokens,
    TopP = TopP,
    Seed = Seed,
    ResponseMimeType = "application/json", // 必须与ResponseSchema配合使用
    ResponseSchema = OpenApiSchema.Parser.ParseFrom(
        BinaryData.FromBytes(
            Encoding.UTF8.GetBytes(@"
{
  ""type"": ""array"",
  ""items"": {
    ""type"": ""object"",
    ""properties"": {
      ""rank"": {""type"": ""integer""},
      ""score"": {""type"": ""integer""},
      ""propertyId"": {""type"": ""integer""},
      ""address"": {""type"": ""string""},
      ""proximity"": {""type"": ""string""},
      ""price"": {""type"": ""string""},
      ""livingArea"": {""type"": ""string""},
      ""lotSize"": {""type"": ""string""},
      ""yearBuilt"": {""type"": ""integer""},
      ""bedrooms"": {""type"": ""integer""},
      ""bathrooms"": {""type"": ""integer""},
      ""notes"": {""type"": ""string""}
    },
    ""required"": [""rank"", ""score"", ""propertyId"", ""address"", ""price"", ""bedrooms"", ""bathrooms""]
  }
}")
        )
    )
}

3. 额外注意事项 #

• 确保使用的Google.Cloud.AIPlatform.V1 SDK版本在1.13.0及以上，该版本才正式支持ResponseSchema特性。
• ResponseMimeType必须设置为application/json，否则ResponseSchema不会生效。
• 如果需要从外部传入Schema，确保传入的是标准JSON字符串，而非自定义类型注解。

内容的提问来源于stack exchange，提问作者Justin