I have an entity that originally started with a date attribute. I have now added a attribute that is a string that I want to hold the date, in addition to keeping the original field.
I've made a mapping model, but I'm not sure what to put into "value expression" to get the new string field filled with data from the date field in the format "2010-10-25" during migration.
Any help would be appreciated.
Also I need it to be a real attribute not a transient because I want to sort on it. I didn't realize you couldn't sort on transient attribute until too late.
Translating the property from a date to a string is going to require that you build your own NSEntityMigrationPolicy for that migration and override the -createDestinationInstancesForSourceInstance: entityMapping: manager: error: method to handle the translation.
This should be very straight forward code since you are only going to be manipulating a couple of properties and the entity mapping is still one to one.
Related
I have a DB First Entity Framework 5 Data Access Layer that is mapped to a table containing a SQL geometry type field called CenterCoordinate. The resulting entity contains this:
public System.Data.Spatial.DbGeometry CenterCoordinate { get; set; }
My client javascript requests the API and only accepts JSON. I then use the Asp.net Web API to serve this using the default formatter (JSON.NET). In the API controller the field has a long list of properties including an XCoordinate and a YCoordinate.
In the client the JSON only contains this:
Geometry: Object
CoordinateSystemId: 3498
WellKnownBinary: null
WellKnownText: "POINT (6438089.715 1801515.828)"
I really don't want to have to parse out the WellKnownText to get to the values of X and Y.
So the question is how can I control the serialisation/de-serialisation of System.Data.Spatial types to/from JSON such that I get something more useful? How does the JSON.net formatter know what to include/exclude?
Note: I really don't want decorate the entity with attributes as these will be lost each time I regenerate the model from the database (I have no idea why we can't add attributes to model fields through VS2012 and have it remember them after a regeneration). So can this be with partial classes or overriding the formatter?
Thanks, Matt
Unfortunately, you're more or less stuck parsing the WellKnownText field if you want to manipulate the coordinates with Javascript.
Geometry is a SQLSpatial type that is saved to a database via the WKT field, so that's why your DbGeometry type is converting the JSON to that format.
If it makes you feel any better, it's causing me just as much of a hassle right now.
Edit: These resources might help a bit:
GeoJSON has a structure much more similar to SpatialSQL:
http://www.geojson.org/geojson-spec.html
https://github.com/Esri/geojson-utils/blob/master/src/jsonConverters.js
This is a solution used to serialize/deserialize DbGeo types as JSON:
http://www.arcgis.com/home/item.html?id=6d28a606369c43fd9a6f929541ae7c93
I know I can solve this by adding another property to my entity which will contain the conversion between types but was wondering if it is possible with EF CF.
Do you need this for UI presentation (of the DateTime value) reasons?
If so, you might want to consider defining a separate View model class, and using something like AutoMapper to map the properties between the two.
I've found two ways of concurrency checking for my entities in EF 4.1:
TimeStamp attribute for byte array
ConcurrencyCheck attribute for another types
The first one is very simple. You just mark byte array property as TimeStamp, create additional column in database and voila...
I've got a problem with the second method. Enity Framework has started generate sql script for concurrency check, when I marked the LastUpdateDate property.
Property:
[ConcurrencyCheck]
public DateTime LastUpdateDate { get; set; }
Sql:
select
...
where (([Id] = #3) and ([LastUpdateDate] = #4))
...
#4='value'
But EF does not generate sql script for updating the value of LastUpdateDate?
Is it possible to say EF to update the LastUpdateDate after concurrency checking without triggers or something like this?
And the second question:
What is the best practice of using concurrency checking in EF when you have something like LastUpdateDate property(property will be displayed in UI)? Is it better to check concurency using LastUpdateDate and avoid creating of addtional column for TimeStamp in your tables or
create additional TimeStamp property and renounce of the using DateTime property for concurrency checking?
Have you tried to use a rowversion (timestamp) instead of the DateTime datatype to check for concurency?
I would use the timestamp, because you are sure that the system will update it for you. Further more the value will be very precice.
The following blog posts will give you more information about how to map a timestamp.
The first one shows how to use the timestamp as a concurrency check.
Code First Optimistic Concurrency with Fluent Assertions
Round tripping a timestamp field with EF4.1 Code First and MVC 3
I want to use a Money value object in my application. I have found several examples of a Money datatype. But I can't figure out how to use them with EF4. I would like to store each amount as a Decimal/CurrencyCode pair (where currencycode is a string - "USD", "SEK", etc) in the database. I tried creating a complexType but I couldn't get that to work. Is this possible?
It should be definitely possible. Your complex type is just pair of decimal and string property. It is exactly what complex type are used for. Depending on your approach you must do:
Database first:
You will define your database first. Your table will contain money and varchar columns representing your new type. When you update your EDMX model from database it will include it as scalar properties to your entity. You must remove those properties. Then go to model browser and create new complex type. Return back to entity and add complex property of your new complex type. And at the end you must go to entity mapping and map your complex type to those database columns.
Here is basic tutorial from MSDN but from unknown reason they didn't include such elementary details like screenshots. Here is some video from channel9.
Model first:
This is similar to database first but you don't have to deal with database creation and mapping. It will be generated for you.
Code first (EF 4.1):
You must create separate class for your complex type and use it as property in your entity. You should not need to map it by default - mapping should be infered. If it doesn't work you can map complext type either by using ComplextTypeAttribute annotation or by defining mapping in DbModelBuilder.
I can further extend approach you need to use if you provide more details.
I have a SQL Server 2008 database. I have a bunch of fields in TableA that are just strings that corresponds to booleans. So every value is either true or false. The edmx I generated using Entity Framework 4.0 has them as strings. This is technically correct but I would like to have them mapped as Booleans instead. Is this possible? If so how can I accomplish this?
Thanks much!
You could create a partial class alongside the generated one and add the bool property there with code to go back and forth from bool to string version. You could also mark the generated property as protected or internal to hide it from the rest of your code.
It's not ideal since the bool property cannot appear in query expressions unless you first force the query to happen using, for example, .ToList().
Your best bet would be to fix the database.