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c# - 如何从 DynamoDb 获取所需格式的对象

问题描述

我有ASP.Net Core（C#）应用程序DynamoDb作为数据库下面是我的函数的样子： -

public async Task<object> GetEvent(string eventId)
    {
        try
        {


            var req = new QueryRequest()
            {
                TableName = _tableName,
                KeyConditionExpression = "EventId = :v_Id",
                ExpressionAttributeValues = new Dictionary<string, AttributeValue>()
                {
                    { ":v_Id", new AttributeValue()
                    {
                        S = eventId
                    } },
                    {
                        ":v_isDeletedFlag",new AttributeValue()
                        {
                            BOOL = false
                        }
                    }
                },
                FilterExpression = "IsDeleted = :v_isDeletedFlag",
                Limit = 1,
            };
            var res = await _dynamoClient.QueryAsync(req);

            if (res.HttpStatusCode == System.Net.HttpStatusCode.OK)
            {

                return res.Items;
            }
            else
            {
                throw new Exception("No such event found");
            }
        }
        catch (Exception ex)
        {
            throw;
        }
    }

但上述方法返回的对象如下：-

[
{
 "CreatedOn": {
  "b": null,
  "bool": false,
  "isBOOLSet": false,
  "bs": [],
  "l": [],
  "isLSet": false,
  "m": {},
  "isMSet": false,
  "n": null,
  "ns": [],
  "null": false,
  "s": "Friday,16 August 2019 14.33.35",
  "ss": []
},
"IsAlcoholAllowed": {
  "b": null,
  "bool": false,
  "isBOOLSet": true,
  "bs": [],
  "l": [],
  "isLSet": false,
  "m": {},
  "isMSet": false,
  "n": null,
  "ns": [],
  "null": false,
  "s": null,
  "ss": []
},
"Description": {
  "b": null,
  "bool": false,
  "isBOOLSet": false,
  "bs": [],
  "l": [],
  "isLSet": false,
  "m": {},
  "isMSet": false,
  "n": null,
  "ns": [],
  "null": false,
  "s": "Hello Events",
  "ss": []
},
"Title": {
  "b": null,
  "bool": false,
  "isBOOLSet": false,
  "bs": [],
  "l": [],
  "isLSet": false,
  "m": {},
  "isMSet": false,
  "n": null,
  "ns": [],
  "null": false,
  "s": "Test Event Mumbai",
  "ss": []
}}]

但我想要的是具有如下键和值的对象

[
{
 "CreatedOn":  "Friday,16 August 2019 14.33.35",
 "IsAlcoholAllowed": false,
  "Description": "Hello Events"
}]

我怎样才能得到这个？

谢谢！

标签： c#amazon-web-servicesasp.net-coreamazon-dynamodbaws-sdk

解决方案

如果我正确理解您的问题，那么您正在使用 Dynamo 的低级编程模型查询数据，这就是为什么您会获得描述每个属性的详细 JSON 的原因。

如果您想更好地控制您的响应，如何使用 DynamoDB 的对象持久性编程模型？

定义一个代表您的文档的模型：

[DynamoDBTable("Events")]
public class Event
{
    [DynamoDBHashKey]   
    public int EventId { get; set; }

    public DateTime CreatedOn { get; set; }

    public bool IsAlcoholAllowed { get; set; }

    public string Description { get; set; }        

    public bool IsDeleted { get; set; }
}

然后通过以下方式查询：

var client = new AmazonDynamoDBClient();
var context = new DynamoDBContext(client);

var filter = new QueryFilter();
filter.AddCondition(Model.HashKey, QueryOperator.Equal, 123);

var events = await context.FromQueryAsync<Event>(new QueryOperationConfig
{
    Select = SelectValues.AllAttributes,
    Filter = filter
});

然后，您可以在 JSON 解析器中传递此模型的列表，从而使您更接近目标数据结构。

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