防止从对象传递未使用的属性的最佳方法

Question

I'm putting together a WCF service that handles a large search (currently 50-60 parameters, with more likely to be added in the future). To handle this, I have a Search object with all the criteria which will be passed to the service in a message object. While all the search parameters must be available, it is often the case that 2-3 of the parameters receive user input and the others are null. To my mind, it doesn't make sense to pass the entire object around through every method if only a few fields are used. I'm looking for a technique that will extract the fields that are used with their values, which can then be validated and passed to the data layer to execute the search. A few ways to accomplish this that I can think of include:

• Use reflection to loop through the properties, and add non-null properties to a Dictionary<string, object> . The problem that comes to mind here is that I lose the type of the search parameter, which means the data layer search function will be one giant case statement with hard-coded cast values for each potential field. This seems to be overkill and creating way too tight of coupling.
• Create a SearchValue class with Name, Value, and System.Type properties, and use reflection to build a List<SearchValue> . This still results in a big case check in the search, but rather than by property it would be by type. This has some appeal in making the process more "generic" (ie, independent of what combination of search values are used), but it also feels like I'm reinventing the wheel.

What pros and cons am I missing with these techniques? Is there a better way to accomplish my goals?

Answer 1

The only problem with passing the whole object around is possible between client and service, when there are too many empty xml nodes in serialized request making it bigger then necessary. Are you trying to handle this? I would say that anyway it is not a big deal and is not worth inventing complicated custom mechanisms.

Answer 2

我不确定这是否适用于此通信线路，但可能是DataMemberAttribute上的EmitDefaultValue属性？

Answer 3

In your first point you mention using Reflection to convert your type to a Dictionary . And on the other side, why not write a reverse logic to convert the Dictionary back to your type using Reflection again?

Example:

Client Side > YourType >>( Reflection )>> Dictionary > Channel > Dictionary >>( Reflection )>> YourType > Server Side

Answer 4

A few options come to my mind:

• Use codegen to create the packing/unpacking code into and out of a Dictionary. The generator code would use reflection, but the packing/unpacking code would not.

• Split your Search class into multiple smaller classes, then have your Search class reference those. Don't instantiate the child classes if those search parameters aren't being used. Perhaps something like:

• • Search
• • • New class containing some common fields
• • • New class containing some other fields

Answer 5

Have a dataContract class with optional datamember.

[DataMember(EmitDefaultValue = false)]

public int salary = 0;

DataContract serializer ignore such member when value is default.

MSDN recommendation: Setting the EmitDefaultValue property to false is not recommended. You should do this only if there is a specific need to do so, such as for interoperability or data size reduction.

You do also have property IsRequired in DataMember, setting it to false and EmitDefaultValue with help reducing transport and serialization overhead.