给定分区键、行键、属性名称和值，如何更新该实体的属性值？

Question

对于azure表，如果我知道实体的RowKey和PartitionKey（这样我就可以检索该实体），我如何编辑该实体上的特定属性值？

这听起来像是一个非常标准的操作，但正常的操作方式是：

public void UpdateEntity(ITableEntity entity)
{
    TableOperation replaceOperation = TableOperation.Replace(entity);
    table.Execute(replaceOperation);
}

即给出整个C#表实体对象作为替换而不是单个属性名称/值对。

我想要更像的东西

public void UpdateEntityProperty<T>(string partitionKey, string rowKey,
                                string propertyName, T newPropertyValue)
{
    TableOperation retrieveOperation = TableOperation.Retrieve(partitionKey, rowKey);
    TableResult retrievedResult = table.Execute(retrieveOperation);
    TableEntity entity = (TableEntity)retrievedResult.Result;
    // This  line, of course, doesn't compile. But you get the idea.
    entity.SetPropertyValue(propertyName, newPropertyValue);
    TableOperation replaceOperation = TableOperation.Replace(entity);
    table.Execute(replaceOperation);
}

我的理解是，在后台，行被存储为一组与该行上的属性相对应的键值对，因此更新属性的值应该很容易，而不必定义从TableEntity派生的整个C#类

我该怎么做？

Answer 1

为了完整起见，以下是我最终使用的内容，灵感来自Gaurav Mantri的答案：

public void UpdateEntityProperty(string partitionKey, string rowKey,
                                 string propertyName, string newPropertyValue)
{
    var entity = new DynamicTableEntity(partitionKey, rowKey);
    var properties = new Dictionary<string, EntityProperty>();
    properties.Add(propertyName, new EntityProperty(newPropertyValue));
    var mergeOperation = TableOperation.Merge(entity);
    table.Execute(mergeOperation);
}

Answer 2

不要执行"替换"操作，而是执行"合并"操作(http://msdn.microsoft.com/en-us/library/windowsazure/microsoft.windowsazure.storage.table.tableoperation.merge)。合并操作将确保只更改正在修改的属性，而不更改所有其他属性。

public void UpdateEntityProperty<T>(string partitionKey, string rowKey,
                                    string propertyName, T newPropertyValue)
{
    TableOperation retrieveOperation = TableOperation.Retrieve(partitionKey, rowKey);
    TableResult retrievedResult = table.Execute(retrieveOperation);
    TableEntity entity = (TableEntity)retrievedResult.Result;
    // This  line, of course, doesn't compile. But you get the idea.
    entity.SetPropertyValue(propertyName, newPropertyValue);
    TableOperation mergeOperation = TableOperation.Merge(entity);
    table.Execute(mergeOperation);
}

下面是一个更完整的例子。在这里，我首先创建了一名员工，然后只更改了该员工的"MaritalStatus"属性：

CloudStorageAccount storageAccount = CloudStorageAccount.DevelopmentStorageAccount;
CloudTable table = storageAccount.CreateCloudTableClient().GetTableReference("Employee");
DynamicTableEntity entity = new DynamicTableEntity()
{
    PartitionKey = "Employee",
    RowKey = "01",
};
Dictionary<string, EntityProperty> properties = new Dictionary<string, EntityProperty>();
properties.Add("Name", new EntityProperty("John Smith"));
properties.Add("DOB", new EntityProperty(new DateTime(1971, 1, 1)));
properties.Add("MaritalStatus", new EntityProperty("Single"));
entity.Properties = properties;
TableOperation insertOperation = TableOperation.Insert(entity);
table.Execute(insertOperation);
DynamicTableEntity updatedEntity = new DynamicTableEntity()
{
    PartitionKey = "Employee",
    RowKey = "01",
    ETag = "*",
};
Dictionary<string, EntityProperty> newProperties = new Dictionary<string, EntityProperty>();
newProperties.Add("MaritalStatus", new EntityProperty("Married"));
updatedEntity.Properties = newProperties;
TableOperation mergeOperation = TableOperation.Merge(updatedEntity);
table.Execute(mergeOperation);

您也可以尝试InsertOrMerge(http://msdn.microsoft.com/en-us/library/windowsazure/microsoft.windowsazure.storage.table.tableoperation.insertormerge.aspx)操作。

Answer 3

试试这个：

if (entity != null)
{
     entity.propertyName = newPropertyValue;
     TableOperation updateOperation = TableOperation.Replace(entity);
     table.Execute(updateOperation);
}