c# - 无法在 Unity 中查询或扫描 DynamoDB

Question

TLDR: Can't create an AsyncSearch object from QueryAsync or ScanAsync without running into a weird ArgumentNullException deep inside the AWS library.

我正在使用 Unity 开发在线游戏，并希望与 DynamoDB 同步数据。当我只有一张包含球员数据的表格时，这非常有效。我只会使用“DBContext.LoadAsync(id, callback);”它完美地工作。使用“SaveAsync”保存同样有效。

现在我又引入了一些表，需要进行扫描和查询。出于测试目的，我为我的 Unity 应用程序提供了它可能拥有的所有权限(我在 IAM 中使用了“dynamodb:*”和“Resource”: [“*”])。

我基本上尝试了具有不同参数的 ScanAsync、QueryAsync 和 FromQueryAsync 的所有可能版本，但我总是遇到错误。

简单的例子:我想下载(我大学的)所有院系:

AsyncSearch<DepartmentData> search = AWSManager.Instance.DBContext.ScanAsync<DepartmentData>();

这个调用已经失败了，我还没来得及做“search.GetRemainingAsync(callback)”之类的事情。这同样适用于简单的查询，例如:

AsyncSearch<POIVisit> query = AWSManager.Instance.DBContext.QueryAsync<POIVisit>(poiType);

错误如下，在 AWS 库的某个深处，所以我不能真正进入那里，设置一些断点并查看到底是什么失败了:

ArgumentNullException: Argument cannot be null.
Parameter name: key
System.Collections.Generic.Dictionary`2[System.Type,Amazon.Runtime.IExceptionHandler].TryGetValue (System.Type key, IExceptionHandler& value) (at /Users/builduser/buildslave/mono/build/mcs/class/corlib/System.Collections.Generic/Dictionary.cs:588)
Amazon.Runtime.Internal.ErrorHandler.ProcessException (IExecutionContext executionContext, System.Exception exception) (at E:/JenkinsWorkspaces/v3-trebuchet-release/AWSDotNetPublic/sdk/src/Core/Amazon.Runtime/Pipeline/ErrorHandler/ErrorHandler.cs:202)
Amazon.Runtime.Internal.ErrorHandler.InvokeSync (IExecutionContext executionContext) (at E:/JenkinsWorkspaces/v3-trebuchet-release/AWSDotNetPublic/sdk/src/Core/Amazon.Runtime/Pipeline/ErrorHandler/ErrorHandler.cs:78)
Amazon.Runtime.Internal.PipelineHandler.InvokeSync (IExecutionContext executionContext) (at E:/JenkinsWorkspaces/v3-trebuchet-release/AWSDotNetPublic/sdk/src/Core/Amazon.Runtime/Pipeline/PipelineHandler.cs:57)
Amazon.Runtime.Internal.CallbackHandler.InvokeSync (IExecutionContext executionContext) (at E:/JenkinsWorkspaces/v3-trebuchet-release/AWSDotNetPublic/sdk/src/Core/Amazon.Runtime/Pipeline/Handlers/CallbackHandler.cs:45)
Amazon.Runtime.Internal.PipelineHandler.InvokeSync (IExecutionContext executionContext) (at E:/JenkinsWorkspaces/v3-trebuchet-release/AWSDotNetPublic/sdk/src/Core/Amazon.Runtime/Pipeline/PipelineHandler.cs:57)
Amazon.Runtime.Internal.Signer.InvokeSync (IExecutionContext executionContext) (at E:/JenkinsWorkspaces/v3-trebuchet-release/AWSDotNetPublic/sdk/src/Core/Amazon.Runtime/Pipeline/Handlers/Signer.cs:38)
Amazon.Runtime.Internal.PipelineHandler.InvokeSync (IExecutionContext executionContext) (at E:/JenkinsWorkspaces/v3-trebuchet-release/AWSDotNetPublic/sdk/src/Core/Amazon.Runtime/Pipeline/PipelineHandler.cs:57)
Amazon.Runtime.Internal.CredentialsRetriever.InvokeSync (IExecutionContext executionContext) (at E:/JenkinsWorkspaces/v3-trebuchet-release/AWSDotNetPublic/sdk/src/Core/Amazon.Runtime/Pipeline/Handlers/CredentialsRetriever.cs:72)
Amazon.Runtime.Internal.PipelineHandler.InvokeSync (IExecutionContext executionContext) (at E:/JenkinsWorkspaces/v3-trebuchet-release/AWSDotNetPublic/sdk/src/Core/Amazon.Runtime/Pipeline/PipelineHandler.cs:57)
Amazon.Runtime.Internal.RetryHandler.InvokeSync (IExecutionContext executionContext) (at E:/JenkinsWorkspaces/v3-trebuchet-release/AWSDotNetPublic/sdk/src/Core/Amazon.Runtime/Pipeline/RetryHandler/RetryHandler.cs:74)

如果我想基于二级索引进行查询，情况会变得更糟。为此，我需要在散列和范围键的条件之后附加一个 DynamoDBOperationConfig，如下所示:

var queryConfig = new DynamoDBOperationConfig() { IndexName = "PlayerIndex" };
AsyncSearch<POIVisit> query = AWSManager.Instance.DBContext.QueryAsync<POIVisit>(poiType, QueryOperator.Equal, PlayerID, queryConfig);

现在，它似乎以某种方式认为，queryConfig 只是范围键的另一个值(因此它基本上选择了错误的 QueryAsync 重载版本)。或者至少我认为会发生这种情况，因为我现在遇到了一个奇怪的转换错误:

InvalidCastException: Cannot cast from source type to destination type.
Amazon.DynamoDBv2.Converter`1[T].TryTo (System.Object value, Amazon.DynamoDBv2.DocumentModel.Primitive& p) (at E:/JenkinsWorkspaces/v3-trebuchet-release/AWSDotNetPublic/sdk/src/Services/DynamoDBv2/Custom/Conversion/DynamoDBEntryConversion.cs:630)
…
Amazon.DynamoDBv2.DataModel.DynamoDBContext.QueryAsync[POIVisit] (System.Object hashKeyValue, QueryOperator op, System.Object[] values) (at E:/JenkinsWorkspaces/v3-trebuchet-release/AWSDotNetPublic/sdk/src/Services/DynamoDBv2/Custom/DataModel/_unity/Context.Async.cs:550)
DBManager.RetrievePlayerVisits (System.String poiType, UnityEngine.Events.UnityAction`1 callback) (at Assets/Scripts/Managers/DBManager.cs:359)

我的 Unity 版本是 5.6.3f1。我尝试了 AWSSDK.DynamoDBv2.3.3.4.18 和旧的 AWSSDK.DynamoDBv2.3.3.4.14 Unity 包，其中包含直接从亚马逊下载的 AWS SDK。

如果有人提示我可能做错了什么，我将不胜感激，谢谢!

Answer 1

您需要在创建查询之前构建一个请求对象。我从未使用过 Unity，但它应该类似于

var request = new QueryRequest();
request.TableName = "YourTable";   
request.KeyConditions = new Dictionary<string, Condition>()
{
    { 
        "YourId",  new Condition()
        { 
            ComparisonOperator = "EQ",
            AttributeValueList = new List<AttributeValue>()
            {
                new AttributeValue { S = YourId }
            }
        }
    }
};

client.QueryAsync(request,(result));

具体来说，您似乎没有将关键条件作为请求的一部分，而这是必需的。