I am trying to create WCF Data service project using Entity Framework. ( I am new to both).
I created entities using DB.
Now, I created service operation, which returns the IQueryable<entity>.
My problem is
I do not want to return the entire set of columns in the entity. I cannot delete them from the entity as it is not null. How to avoid these?
I have few FK columns and I need other column details of the table. How to include columns from other table?
Why it is not possible to use POCO class to be returned from WCF Data service?
How do I format the response; i.e., add few more details to the response like page number etc, change the xml tags, remove few details like "link rel"?
I have tried a lot of things to achieve 1 and 2. But finally I realised that I can only use the entity as it is to make it work.
I have no idea about 4.
Any suggestions would be appreciated.
1. I do not want to return the entire set of columns in the entity.
2. I have few FK columns and I need other column details of the
table.
For this, you should define a new class that matches what you need / what you want your clients to see. That can be a straight POCO class - no special requirements. Assemble that class for each entity, leaving out the unwanted columns, and grabbing the extra field or two for the FK columns into that new class. Return an IQueryable<YourNewClass> instead of the entity class directly.
To avoid huge left-right-assignment statements just to fill the properties of the new class, you should have a look at AutoMapper which makes it really easy to copy around classes that are very similar to one another (e.g. missing or adding a few properties).
4. How do I format the response; i.e., add few more details to the
response like page number etc, change the xml tags, remove few details
like "link rel"?
That's not possible - the OData protocol very strictly defines what's going to be in the message, what links there are etc. If you can't live with that - you'll have to roll your own WCF REST service and drop the WCF Data Service stuff altogether.
Check out the WCF REST Developer Center on MSDN if you want to investigate that route more thoroughly.
Update: that link seems to have gone dead - try WCF Web Http Programming Overview instead.
Make sure you have an Id property or you specify either [Key] or [DataServiceKey("Your_Custom_ID_Property")]
For me this sorted out the issue
Related
I have a problem that's probably easy to fix, but I don't find the right way to do it.
I have the following situation:
I am building a web application where I use several forms. One of the forms uses and displays two Entity Framework models that have a 1:1 relation. It's one entity for all BaseData (common Data) and one entity for AdditionalData (specific Data). The form's Model is of type AdditionalData, which has a NavigationProperty of type BaseData.
When I want to save this "form" i.e. the two entities - what is the best way to do that?
Do I call two Actions seperately, like "Save(BaseData) then Save(AdditionalData)"(how?)?
Do I redirect from one Save Action to the Other one (also how?)?
Do I need to build a new Model to accomplish what I need (maybe with a special ModelBinder) or do I only need a special ModelBinder?
Can I manually invoke the ModelBinder for the "BaseData" manually from the Save Action of the AddidionalDataController?
Am I doing it completely wrong in the first place?
Thank you for any help!
We would like to create an OData REST API. Our data model is such that each customer has their own database. All database objects have the same definition across all customer databases, with the exception of a single table.
The customer specific table we will call Contact. When a customer adds a column the system creates a column with a standardised name with a definition translated from options selected by the user in the UI. The user only refers to the column data by a field name they have specified to enable the user to be able to generate friendly queries.
It seems to me that the following approaches could be used to enable OData for the model described:
1) Create an OData open type to cater for the dynamic properties. This has the disadvantage of user requests for a customer not providing an indication of the dynamic properties that can be queried against. Even though they will be known for the user (via token authentication). Also, because dynamic properties are a dictionary, some data pivoting and inefficient query writing would be required. Not sure how to implement the IQueryable handling of query options for the dynamic properties to enable our own custom field querying.
2) Create a POCO class with e.g. 50 properties; CustomField1, CustomField2... Then somehow control which fields are exposed for use in OData calls. We would then include a separate API call to expose the custom field mapping. E.g. custom field friendly name of MobileNumber = CustomField12.
3) At runtime, check to see if column definitions of table changed since last check. If have, generate class specific to customer using CodeDom and register it with OData. Aiming for a unique URL for each customer. E.g. http://domain.name/{customer guid}/odata
I think the ideal for us is option 2. However, the fact the CustomField1 could be an underlying SQL data type of nvarchar, int, decimal, datetime, etc, there are added complications.
Has anyone a working example of how to achieve what has been described, satisfactorily?
Thanks in advance for any help.
Rik
We have run into a similar situation but with our entire dataset being unknown until runtime. Using the ODataConventionModelBuilder and EdmModel classes, you can add properties dynamically to the model at runtime.
I'm not sure whether you will have to manually add all of the properties for this object type even though only some of them are unknown or whether you can add your main object and then add your dynamic ones afterwards, but I guess either would be workable.
If you can get hold of which type of user it is on the server, you could then add only the properties that you are interested in (like option 3 but not having to CodeDom).
There is an example of this kind of untyped OData server in the OData samples here that should get you started: https://github.com/OData/ODataSamples/tree/master/WebApi/v4/ODataUntypedSample
The research we carried out actually posed Option 1 as the most suitable approach for some operations. i.e. Create an SQL view that unpivots the data in a table to a key/value pair of column name/column value for each column in the table. This was suitable for queries returning small datasets. This was far less effort than Option 3 and less confusing for the user than Option 2. The unpivot query converted the field values to nvarchar (string) values and thus meant that filtering in the UI by column value data types was not simple to achieve. (If we decide to implement this ability, I believe this can be achieved by creating a custom attribute that derives from EnablQueryAttribute, marking the controller action with it and manipulate the IQueryable before execution).
However, we wanted to expose a /Contacts/Export endpoint that when called would output the columns from a table with a fixed schema joined on a table with a client specific schema and output to a CSV file. All the while utilising the OData supported filter syntax. One of our customer databases has more than 12 million rows of data and is made up of approximately 30 columns.
To achieve this it looks like our best bet would have been to work with the Microsoft.OData.Core.UriParser.UriQueryExpressionParser class, unfortunately Microsoft in their wisdom have declared this as internal, as well as many of it's dependants.
Walking an abstract syntax tree built from OData supported query options and applying our own visitor to each node to build some dynamic Linq query/SQL seems like a possible solution.
For the time-being we will simply implement a cut-down set of supported $filter criteria without the support for grouping parenthesis.
I am developing a SPA using Angular-Breeze-WebAPI-EntityFramework.
Now Breeze uses the Entity Framework metadata information to create it's own Breeze models. We use this in our application for Breeze validation.
So far, it's all been nice and easy. Now we are having to create a search page (say for querying customers). The search can be by Customer.Name or by Product.Id (which would return a list of customers who have bought that product). The result is a ng-repeater, which displays Customer.Name, Order.LastPlaced etc.
if you are getting confused by the tables and columns, forget that. What I am only trying to get to is that, both the search object and the result object are not 1:1 with Entity tables (or objects). So obviously I feel the need to create a custom object (one for the search and one for the results). My question primarily is where and how do I create that object?
If I create it at the data layer, Breeze would have no idea of the metadata for each of the properties (since it uses EF for that).
I obviously can't create just a JavaScript object, since I will have to query the database (using EF) to search and populate the object.
So where does one create such a custom object (traversing multiple tables) such that Breeze still can figure out the metadata and perform validation and such when the need arises?
Thank you all.
You can create metadata on the client for types that the server either doesn't know about or doesn't have the schema for. See http://www.breezejs.com/documentation/metadata-by-hand.
I have an Entity called "Product", this entity, through table mapping, merges 6 tables that have a 1 to 1..0 relationship with "Products". This all works wonderfully. There is another property I want to add to "Products", which is sBBR_rate, this value is not in a table that has a direct 1 to 1..0 relationship, it is related through a link table as below:
When I import the two tables into the EDM, I can't see a way in the "Mapping Details" of
"Product" to reference the sBBR_rate. I can reference RatesLink and link that to the "Products" primary key, however, I cannot reference the BBR table.
The methods I can think of to work "around" this is are as follows:
Create a view, reference the view in the EDM.
Create an SP and use a function import to retrieve the BBR when it is required.
Create a "Rates" entity in the EDM that can then draw down the sBBR_rate into it. Navigate to the Products BBR through Product.Rates.sBBR_rate.
Is there a better way I can do this that doesn't feel so much like a fudge? Perhaps by directly editing the XML of the Mapping or Conceptual layers of the EDM?
Thanks for your input.
Because the multiplicities on the Product -> RatesLink and RatesLink -> BBR relationships are 0 to 1, you should be able to access the sBBR_rate from a Product instance like this:
myProductInstance.RatesLink.BBR.sBBR_rate
I can see on the EDM screenshot that RatesLink has a Product and BBR property, which would indicate this should be available - is it?
On a side note, if it makes sense for the sBBR_rate property to commonly be accessed directly from Product, you might want to follow the law of demeter and create a property on Product which returns it directly.
The model we are using is to extend entities by using partial classes which we've found useful so we can get additional properties in the autogenerated classes (we are using a POCO T4 template to autogen but I believe this would work just as well with the default entity object generation).
So we would have
//.. this one is from the T4 template
public partial class Product
{
//.. all the autogenerated methods
}
and in a separate file that isn't autogened
//.. now in a separate file created by me
public partial class Product
{
//.. my custom properties and methods to make the entities more usable
public string BBRRate
{
get {return this.RatesLink.BBR.sBBR_rate; }
}
}
This means that I can just do
myProduct.BBRRte
I know there are other ways to do this by amending the edmx file but this one we found easy to implement. You just need to watch performance because you are potentially loading extra data. Also we did this with LazyLoading turned on but with more work you wouldn't have to
We also experimented with hooking into the ObjectMaterialized event in the ObjectContext class to preload some of these properties. Using a custom interface i.e. IMaterialisable we could check if the object was of that type then call a method (Materialise) to prepopulate some of the properties. This seems like a good idea but we didn't widely use it - it was easy to load up too much stuff. If you do the load on the properties in the partial classes then it becomes more efficient. Just my experience.
Anyway - as always an interesting question and good luck again with your dev.
EDIT
There is a rule that everything in the store layer must be represented some way in your conceptual layer. Therefore removing the tables from the conceptual layer but bring through some of the properties I don't think will work in it's gross form. Therefore I can think of two further options
Create a View on the database and bring that in as you have already mentioned. TBH this is what I would do.
Use the DefiningQuery element directly in your xml (the store layer) and map the query through to a custom entity of your exact design. Julie Lerman describes this as the ultimate escape hatch for Entity Framework.
Remember though - if you manual amend the XML in point 2 then you lose the ability to automatically update the module through the IDE
I ended up creating a view and then linking this view in the EDM, this worked a treat.
I'm working on a C#.NET 3.5 WCF RIA Services app and having an issue with my Entity Framework model.
My entity Foo is mapped to a DB table and has a primary key called FooId. My Bar is mapped to a DB view. I've selectively designed this view to generate a composite key in the EF using two of the columns (by making sure they were non-nullable and the others are all nullable. This was done using NULLIF and ISNULL in the view design.)
I'm able to add this view to the model with no problem but I keep running into an issue when I try to map an association between the two. Foo should contain many Bars but I keep getting the following error when I add the association:
Unable to retrieve AssociationType for
association 'FK_Bar_Foo'
According to this page, it looks like this might work if I can properly name the association (since RIA Services looks for specific names.) I've tried several variants of names that match the pattern of other associations with no success. Does anyone know if there's a place I can look to find out what name it's looking for?
Thanks,
After some research I found a workaround to the issue here. The problem with this solution is that you have to repeat it every time the model is updated, which just won't work for me. It appears the current version of the EF doesn't support this type of relation.
The solution I finally went with was to redesign the client to independently call the service and request an entity collection by passing the primary key (FooId) of my Foo type. It's not the best approach (and requires a lot more manual coding) but it does the job. I hope Entity Framework version 4 solves this limitation.