Azure Table storage 之改进DynamicTableEntity类为其添加动态语言扩展
在之前的一篇文章中提到，storage类库中包含一个可以用来动态获取Azure table storage 表结构的类-DynamicTableEntity。
我们可以通过这个类，我们无需为每一个表提前声明一个class，也能够对其进行操作。
但在我们要添加Entity到表中的时候会感觉到一点不舒服
以下我所希望使用的该类的方式：
dynamic entity = new DynamicTableEntity(); entity.Name=”sam”; entity.Gender=true; …
这样的形式
而实际代码却是
DynamicTableEntity entity1 = new DynamicTableEntity();
Dictionary<string, EntityProperty> data1 = new Dictionary<string, EntityProperty>();
data1.Add("Name", new EntityProperty("Sam"));
data1.Add("Gender", new EntityProperty(true));
data1.Add("Age", new EntityProperty(18));
entity1.Properties = data1;
entity1.PartitionKey = "Partition1";
entity1.RowKey = "1";
UserDataList.Add(entity1);
身为一个以dynamic开头的类居然不能够用dynamic关键字来初始化它，在实例化一个DynamicTableEntity类的时候居然要如此麻烦，实在让人不爽。
所以， 经过一番研究，发现了一个可以支持动态扩展的类，为了与DynamicTableEntity区分开来，所以取名DynamicObjectTableEntity。它实现了DynamicTableEntity相同的功能，而且继承了DynamicObject，从而具有动态语言的特性，更加方便 使用。
而且动态语言扩展一直以来除了在linq中使用比较多以外，其它地方基本看不到。这里正好通过对dynamicTableEntity的改造可以加深对动态语言扩展的理解。
实现代码如下：
public class DynamicObjectTableEntity : DynamicObject,ITableEntity
{
#region DynamicTableEntity's code
// Methods
public DynamicObjectTableEntity()
{
this.Properties = new Dictionary<string, EntityProperty>();
}
public DynamicObjectTableEntity(string partitionKey, string rowKey) : this(partitionKey, rowKey, DateTimeOffset.MinValue, null, new Dictionary<string, EntityProperty>())
{
}
public DynamicObjectTableEntity(string partitionKey, string rowKey, string etag, IDictionary<string, EntityProperty> properties) : this(partitionKey, rowKey, DateTimeOffset.MinValue, etag, properties)
{
}
internal DynamicObjectTableEntity(string partitionKey, string rowKey, DateTimeOffset timestamp, string etag, IDictionary<string, EntityProperty> properties)
{
//CommonUtility.AssertNotNull("partitionKey", partitionKey);
//CommonUtility.AssertNotNull("rowKey", rowKey);
//CommonUtility.AssertNotNull("properties", properties);
this.PartitionKey = partitionKey;
this.RowKey = rowKey;
this.Timestamp = timestamp;
this.ETag = etag;
this.Properties = properties;
}
public void ReadEntity(IDictionary<string, EntityProperty> properties, OperationContext operationContext)
{
this.Properties = properties;
}
public IDictionary<string, EntityProperty> WriteEntity(OperationContext operationContext)
{
return this.Properties;
}
// Properties
public string ETag { get; set; }
public EntityProperty this[string key]
{
get
{
return this.Properties[key];
}
set
{
this.Properties[key] = value;
}
}
public string PartitionKey { get; set; }
public IDictionary<string, EntityProperty> Properties { get; set; }
public string RowKey { get; set; }
public DateTimeOffset Timestamp { get; set; }
#endregion
#region override DynamicObject's mehtods
public override bool TryGetMember(GetMemberBinder binder, out object result)
{
if (!Properties.ContainsKey(binder.Name))
Properties.Add(binder.Name, ConvertToEntityProperty(binder.Name, null));
result = Properties[binder.Name];
return true;
}
public override bool TrySetMember(SetMemberBinder binder, object value)
{
EntityProperty property = ConvertToEntityProperty(binder.Name, value);
if (Properties.ContainsKey(binder.Name))
Properties[binder.Name] = property;
else
Properties.Add(binder.Name, property);
return true;
}
/// <summary>
/// Convert object value to EntityProperty.
/// </summary>
private EntityProperty ConvertToEntityProperty(string key, object value)
{
if (value == null) return new EntityProperty((string)null);
if (value.GetType() == typeof(byte[]))
return new EntityProperty((byte[])value);
if (value.GetType() == typeof(bool))
return new EntityProperty((bool)value);
if (value.GetType() == typeof(DateTimeOffset))
return new EntityProperty((DateTimeOffset)value);
if (value.GetType() == typeof(DateTime))
return new EntityProperty((DateTime)value);
if (value.GetType() == typeof(double))
return new EntityProperty((double)value);
if (value.GetType() == typeof(Guid))
return new EntityProperty((Guid)value);
if (value.GetType() == typeof(int))
return new EntityProperty((int)value);
if (value.GetType() == typeof(long))
return new EntityProperty((long)value);
if (value.GetType() == typeof(string))
return new EntityProperty((string)value);
throw new Exception("This value type" + value.GetType() + " for " + key);
throw new Exception(string.Format("This value type {0} is not supported for {1}", key));
}
/// <summary>
/// Get the edm type, if the type is not a edm type throw a exception.
/// </summary>
private Type GetType(EdmType edmType)
{
switch (edmType)
{
case EdmType.Binary:
return typeof(byte[]);
case EdmType.Boolean:
return typeof(bool);
case EdmType.DateTime:
return typeof(DateTime);
case EdmType.Double:
return typeof(double);
case EdmType.Guid:
return typeof(Guid);
case EdmType.Int32:
return typeof(int);
case EdmType.Int64:
return typeof(long);
case EdmType.String:
return typeof(string);
default: throw new TypeLoadException(string.Format("not supported edmType:{0}", edmType));
}
}
#endregion
}
在使用了如下类之后，我们就可以用我预期的代码来操作table 了
代码如下：
static void Main(string[] args)
{
var connectionString = "DefaultEndpointsProtocol=https;AccountName=[Account];AccountKey=[Key]";
CloudStorageAccount storageAccount = CloudStorageAccount.Parse(connectionString);
try
{
var client = storageAccount.CreateCloudTableClient();
var table = client.GetTableReference("ShortMessages");
table.CreateIfNotExists();
dynamic entity = new DynamicObjectTableEntity("default", DateTime.Now.ToShortTimeString());
entity.Name = "pete";
entity.Message = "Hello";
table.Execute(TableOperation.Insert(entity));
Console.WriteLine("insert successfully!");
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
}
Console.Read();
}
示例参考MSDN：http://code.msdn.microsoft.com/Dynamic-TableServiceEntity-151d661f
