I'm developing an application that does some CRUD operations through a WCF service. The read method returns a complete entity, the update is performed through a legacy system, and only the changed values should be updated.
What is the best way to design the data contract for this scenario without simply sending a dictionary of key-value pairs?
The only other thing I can think of is to make your component durable - i.e. persist its state to a file or database. That way, on the update you can compare the previous state to the state being passed in. I'm not sure that's a good way to go since it will introduce more overhead than just passing in the key-value pairs.
From the outside it might look more CRUDy or whatever, but from a practical standpoint you may be better off just passing some indication as to which values changed.
In case it helps, not sure exactly what you're looking for though ...
In the update request, only act upon fields that are not null.
In addition wrap any non-nullable types in a nullable structure.
As an example ...
Update( Nullable<int> orderNumber,
Nullable<DateTime> orderDate,
Nullable<bool> isComplete )
{
if( orderNumber != null )
databaseRecord.OrderNumber = orderNumber;
if( orderDate != null )
databaseRecord.OrderDate = orderDate;
if( isComplete != null )
databaseRecord.IsComplete = isComplete;
}
the best way to do this is with property dictionary, just represent your entities as dictionary of property name and value.
save all changes in some list and pass a partial dictionary with all changed properties.
i think this is best design,
if u wanna avoid this design, send entire entity with some list of changed properties.
(to save transport u can put null on other properties)
if u don't wanna change the service contract signature u can push the names of modified properties on the header
I had two ideas of how to achieve this;
Have the client send both the original entity, and the changed entity in full, the service would then figure out what properties were changed.
Use a pattern similar to Nullable, lets call it Modified with an IsModified flag and a NewValue property of type T. Each property of the DataContract would be of this type, the service can check the IsModified flag when performing the update.
The legacy sytem we use has an api that accepts String.Empty to identify unmodified fields, a '?' character is used to indicate an update to an empty string. I really don't like this, the user of the api is forced to read the documentation, and if you actually want to store a '?' you can't. I want our webservice api to be more explicit.
You can use DataSet to keep your changes. Call your record as DataSet then assign some values to the record. DataSet.Tables[0].GetChanges() will give you the columns which were changed.
You could leave the data contract alone and update your service contract. Just represent the required fields for the method as properties within the service contract. Any consuming application using the service will have to be updated if the service contact changes, but the consuming application will know what is required to successfully update the data.
There are positives and negatives to this method, but I use it when a method I am writing doesn't require the full data contract.
--Edited for a spelling error--
Looking at your requirements and statements, i've made a few assumptions before starting to write my vision on a possible solution:
You are using the same class for retrieving (return value type of "read" operation) and updating an item (input parameter type of "update" operation) in your WCF service.
Your current problem of implementation is how to use the original class (not a dictionary) AND still be able to determine 'what has changed compared to the read' when you get the "Update" operation called on your WCF service
You are writing both the server and client. Both are written using the MS .Net framework.
If this is true, the problem lies in the Update method missing information. The information required is 'has changed' which could be inferred if a 2nd state is present to compare against or should already be present along side the state to update in the back-end.
Since you only have the 'back-end state' (without flags) when the client posts its data to the WCF service, how should we determine what did change? Obviously, we want to prevent another 'read' roundtrip to get the current server state and start comparing.
Sending the original & changed state from the client to the server is a possible but heavy solution. Next to that, the client isn't interrested in this information, the server is.
Adding this all up makes my guess is that changing the type of the 'Update' operation input parameter is the easiest way to go. Create a decorator class that adds 'dirty bit' behavior to the original entity. Use this new class as input parameter for your "Update" operation. You then will have the availability in the server to check this dirty bit next to the full state send by the client. The major change on the client side is that the object needed for the 'Update' operation is no longer the same as the one provided by the 'Read' method. To eleviate this pain, i would probably create a decorator class which added the required 'dirty bit' handling. This only requires the object instanciation to change, while maintaining the interface signature for the client (very little code changes).
Related
Is it possible to indicate a property is a required field without using data annotation attributes?
Instead of using annotation attributes, I want to set it as a required field, based on particular conditions.
For eg, something like below
if (true)
{
//set myObj.Name as required field
}
Edit: The reason why I need to do is, I'm calling a business service class of our own framework, which I can not touch, and inside the class, when the entity is being saved, mandatory checking is already catered.
But, in my requirement, I need to save my entity several times and , each times, the mandatory checking may be different . That's the reason why I need to mark the properties required fields dynamically.
Otherwise, I have to made my own mandatory checking before calling the business service class, which I don't want to do.
From your description, it seems like you need to provide your "own mandatory checking". I say this for two reasons;
To provide your user meaningful feedback as to why something field is required
Also, to satisfy the contract of your business service class
Can you have a "validate" method that simply runs through your set of rules (that mandatory checking, that you mentioned earlier) and have it return a list of strings indicating the rules that were violated on an attempt to save. Then you can use these strings to populate the text of a message box, logfile or whatever to provide meaningful feedback to the user as to why something wasn't saved, and also ensuring that data that is saved, is compliant to your business service class.
I have a requirement where based on the Class Name passed as string from a Third party application, I want to get all properties and its value and assign their values to another object having members with similar names. Now I know this can be done without any issue in a Win Form application but I want to know what all issues will be there if I use this approach in an ASP.NET application - I am not much concerned with the Performance but specifically with the Concurrency (if any possible)
I am using code something like as below:
//Just a Sample Code
Type type = Type.GetType("MyClassName");
var propValue = type.GetProperty("MyProperyName").GetValue(myObject);
Any help will be appreciated.
Concurrency Issues like Race condition etc will come into picture if you are writing or making changes to the values, here you only reading properties, which are already added to metadata of type (Type definition, property definition) tables when you compile your code.
And there is no way you can alter that definition at runtime as long as I know, so the things you are doing is thread safe as long as your type and propvalues are local to thread executing.
Hello fellow developers.
First of all I apologize beforehand for the wall of text that follows, but after a day going crazy on this, I need to call for help.
I've stumbled across a problem I cannot seem to solve. I'll try to describe the scenario in the best possible way.
Task at hand: in an existing Asp.Net Mvc application, create a lookup table for an integer field, and use the textual value from the lookup in the editing view. When saving, we must first check if the lookup already has a corresponding text value for the same Root ID. If there is, use that. Otherwise, create it and then use it.
The structure:
The data model is a graph of objects where we have the root object, a collection of level A child objects, and every level A child object has a collection of level B child objects, so something like this:
Root (with fields)
Level A child (with fields) x n
Level B child (with fields) x n
The field we have to handle is on the LevelB objects.
There is a single Mvc view that handles the whole data. For collection objects, all fields are named like levelA1levelB1MyField, levelA1levelB2MyField, etc so every single field has unique name during the post. When the post happens, all values are read through a formCollection parameter which has average 120/130 keys. The keys are isolated by splitting them and looping on the numerical part of the names, values are read and parsed to the expected types and assigned to the object graph.
The datalayer part backing the object graph is all stored procedures, and all the mapping (both object to sproc and sproc to object) is hand written. There's a single stored procedure for the read part, which gets multiple datasets, and the method calling it reads the datasets and creates the object graph.
For the saving, there are multiple sprocs, mainly a "CreateRoot" and "UpdateRoot". When the code has to perform such tasks, the following happens:
For create scenario, "CreateRoot" is called, then the sprocs "CreateLevelA" and "CreateLevelB" are called in loop for each element in the graph;
For update scenario, "UpdateRoot" is called, which internally deletes all "LevelA" and "LevelB" items, then the code recreates them calling the aforementioned sprocs in loop.
Last useful piece of information is that the "business objects graph" is used directly as a viewmodel in the view, instead of being mapped to a plain "html friendly" viewmodel. This is maybe what is causing me the most trouble.
So now the textbox on the view handles an "integer" field. That field must now accept a string. The field on LevelB must remain an integer, only with a lookup table (with FK of course) and the text field from the lookup must be used.
The approaches I tried with no success:
My first thought was to change the datatype on the property MyField from integer to string on the object, then change the sprocs accordingly and handle the join at sproc level: I'd have a consistent object for my view, and the read/write sprocs could translate from string to integer and viceversa, but I can't do that because the join keys to retrieve the integer when writing are part of the Root item (as I stated in the first lines of this wall of text), which I don't know in the CreateLevelB sproc, and changing the whole chain of calls to pass those parameters would have a huge impact on the rest of the application, so no good.
My next try was to keep things "as they are" and call some "translation methods": when reading, pass the integer to the view, and there call the translation method to display the text value. When saving, use the posted text to retrieve the integer. The save part would work, I'd have all the parameters I need, but for the read part, I'd have to instantiate the "data access layer" and call its method at View level, and there's no need to explain why that is a very bad choice, so I ruled this out too.
Now I'm out of options (or ideas anyway). Any suggestion to solve this is very welcome, and also if something is not clear enough just point it out and I will edit my post with more accurate information.
Thanks.
This is not a real answer but you could rip out all sprocs and use the updating facilities of an OR mapper. This will resolve all the layering issues. You just update data how you see fit and submit at the end.
I guess this would also make the questions around "should I use an int or a string" go away.
Edit: After reading your comment I thought of the following: Do not implement alternative 1. You rather want to sacrifice code quality in the view than in the data storage model. The last one is more important and more centrally used.
I would not be too concerned with messing up the view by calling the DAL from it or the like. Changes in a view are localized and do not mess up the application's architecture. They just degrade the view.
Maybe you could create a view model in your controller and do the translations between DAL-model and view model? Or is that pattern not allowed?
I need to hook into an event in a slightly unusual manner in WCF.
I'm passing a model from the client to the server, and I need access to that model:
After the model has been created but
Before the incoming data has actually been deserialized to that model
The reason is I actually have deserialization events that are conditional, and ideally I want that condition itself to be a property on the object; thus, I'd have the pattern:
create object->set property->deserialize the rest of the object based
on that property
Is there an event in WCF that I can hook into for this? I've got an attribute set up that hooks into the "IOperationBehavior" and "IParameterInspector" set up, but those don't (as far as I can tell) have an action that hooks in between the creation and deserialization events.
Alternatively, I'd be fine with a way of modifying the data coming in off the wire and explicitly adding that property into the incoming data, provided I could guarantee that it would be the first property deserialized.
Any ideas?
[Edit]
Minor note, I'm using JSON as the data transport here, not that that should really have an impact on the final solution.
You could theoretically implement a nested envelope, whereby the actual data passed to your WCF service consists of a class (the envelope) which has the data needed to determine how to deserialize and a byte array which consists of the real data in a serialized format. Then you could manage the deserialization of the byte array manually.
Seems there is probably a better way, but I've done similar things and they work.
EDIT: Perhaps an IDispatchMessageInspector is the right place to hook?
I want to make a Configuration Data Manager. This would allow multiple services to store and access configuration data that is common to all of them.
For the purposes of the Manager, I've decided to create a configuration class object - basically what every configuration data entry would look like:
Name, type, and value.
In the object these would all be strings that discribe the configuration data object itself. Once it has gotten this data from its database as strings, it would put it into this configuration object.
Then, I want it to send it through WCF to its destination. BUT, I don't want to send a serialized version of the configuration object, but rather a serialized version of the object discribed by the configuration object.
The reason I'd like to do this is so that
The Data Manager does not need to know anything about the configuration data.
So I can add configuration objects easily without changing the service. Of course, I should be able to do all of the CRUD operations, not just read.
Summary:
Input: string of name, type and value
Output: Serialized output of the object; the object itself is "type name = value"
Questions:
Is this a good method for storing and accessing the data?
How can I/can I serialize in this manner?
What would the function prototype of a getConfigurationData method look like?
I have decided to go in a different direction, thanks for the help.
Is this a good method for storing and accessing the data?
That is difficult to answer, the best I can give you is both a "yes" and a "No". Yes, It's not a bad idea to isolate the serialization/rehydration of this data.... and No, I don't really care much for the way you describe doing it. I'm not sure I would want it stored in text unless I plan on editing it by hand, and if I'm editing it by hand, I'm not sure I'd want it in a database. It could be done; just not sure you're really on the right track yet.
How can I/can I serialize in this manner?
Don't build your own, never that. Use a well-known format that already exists. Either XML or JSON will serve for hand-editable, or there are several binary formats (BSON, protobuffers) if you do not need to be able to edit it.
What would the function prototype of a getConfigurationData method look like?
I would first break-down the 'general' aka common configuration into a seperate call from the service specific configuration. This enables getConfigurationData to simply return a rich type for common information. Then either add a extra param and property for service specific data, or add another method. As an example:
[DataContract]
public class ConfigurationInfo
{
[DataMember]
public string Foo;
...
// This string is a json/xml blob specific to the 'svcType' parameter
[DataMember]
public string ServiceConfig;
}
[DataContract]
public interface IServiceHost
{
ConfigurationInfo GetConfigurationData(string svcType);
}
Obviously you place a little burden on the caller to parse the 'ServiceConfig'; however, your server can treat it as an opaque string value. It's only job is to associate it with the appropriate svcType and store/fetch the correct value.