I have already tried use polymorphic in greenDao, but not successful.
How to use polymorphic in greenDao ?
for example:
I have a table "my_favorites", in that i can store id foreign key of Events, Pictures, Music ... ?
I hope for your help!
I'm afraid this is not supported by greendao at the moment.
You will have to store the keys to a normal 'LongProperty' without any 'toOne' or 'toMany' and in a second column you will have to save a discriminator value (i.e. the referenced classname).
Then you will have to build the queries yourself (i.e. in the 'KEEP-SECTION' of your 'my_favorites'.
public Object getDetail() throws ClassNotFoundException {
if (daoSession== null) {
throw new DaoException("Entity is detached from DAO context");
}
return daoSession.load(Class.forName(getDiscriminator()), getMyDetailId());
}
you can use ToMany relation in your DB. Look at this tutorial
Entity customer = schema.addEntity("Customer");
customer.addIdProperty();
customer.addStringProperty("name").notNull();
Entity order = schema.addEntity("Order");
order.setTableName("ORDERS"); // "ORDER" is a reserved keyword
order.addIdProperty();
Property orderDate = order.addDateProperty("date").getProperty();
Property customerId = order.addLongProperty("customerId").notNull().getProperty();
order.addToOne(customer, customerId);
ToMany customerToOrders = customer.addToMany(order, customerId);
customerToOrders.setName("orders");
customerToOrders.orderAsc(orderDate);
Related
I am trying to use a property on a POCO that uses LINQ to ENTITY to pull the first object out of a HashSet property on the same POCO. My object contains the following:
public virtual HashSet<ScheduleWaypoint> ScheduleWaypoints { get; set; }
public ScheduleWaypoint ArrivalStation {
get {
if (this.ScheduleWaypoints != null && this.ScheduleWaypoints.Count() > 0) {
return this.ScheduleWaypoints.Where(row => row.WaypointType.Type.Trim() == "SA").OrderByDescending(row => row.ScheduledTime).First();
} else
return null;
}
}
If I were working with just one object I can't say for certain if this would work but I know that it does not work inside other linq queries. I don't have access to the ID of the ScheduleWaypoint when creating the object, only after it is populated could I possibly do that. Is there a way that I can get this to work? Right now it is telling me:
The specified type member 'ArivalStation' is not supported in LINQ to
Entities. Only initializers, entity members, and entity navigation
properties are supported.
Is there something I can do to get access to this information on a property rather than constantly doing joins when I need the info?
Thanks.
You cannot use custom properties in linq-to-entities query. Only properties mapped directly to the database can be used = you must have sub query directly in your linq-to-entities query returning your ArrivalStation. Perhaps it can be wrapped as simple extension method:
public static IQueryable<ScheduleWaypoint> GetArrivalStation(this IQueryable<ScheduleWaypoints> waypoints, int routeId)
{
return waypoints.Where(w => w.WaypointType.Type.Trim() == "SA" && w.Route.Id == routeId)
.OrderByDescending(w => w.ScheduledTime)
.FirstOrDefault();
}
Where Route is your principal entity where way points are defined. FirstOrDefault is used because sub queries cannot use just First.
Is there a way to get EF CTP5 to create an index when it creates a schema?
Update: See here for how EF 6.1 handles this (as pointed out by juFo below).
You can take advantage of the new CTP5’s ExecuteSqlCommand method on Database class which allows raw SQL commands to be executed against the database.
The best place to invoke SqlCommand method for this purpose is inside a Seed method that has been overridden in a custom Initializer class. For example:
protected override void Seed(EntityMappingContext context)
{
context.Database.ExecuteSqlCommand("CREATE INDEX IX_NAME ON ...");
}
As some mentioned in the comments to Mortezas answer there is a CreateIndex/DropIndex method if you use migrations.
But if you are in "debug"/development mode and is changing the schema all the time and are recreating the database every time you can use the example mentioned in Morteza answer.
To make it a little easier, I have written a very simple extension method to make it strongly typed, as inspiration that I want to share with anyone who reads this question and maybe would like this approach aswell. Just change it to fit your needs and way of naming indexes.
You use it like this: context.Database.CreateUniqueIndex<User>(x => x.Name);
.
public static void CreateUniqueIndex<TModel>(this Database database, Expression<Func<TModel, object>> expression)
{
if (database == null)
throw new ArgumentNullException("database");
// Assumes singular table name matching the name of the Model type
var tableName = typeof(TModel).Name;
var columnName = GetLambdaExpressionName(expression.Body);
var indexName = string.Format("IX_{0}_{1}", tableName, columnName);
var createIndexSql = string.Format("CREATE UNIQUE INDEX {0} ON {1} ({2})", indexName, tableName, columnName);
database.ExecuteSqlCommand(createIndexSql);
}
public static string GetLambdaExpressionName(Expression expression)
{
MemberExpression memberExp = expression as MemberExpression;
if (memberExp == null)
{
// Check if it is an UnaryExpression and unwrap it
var unaryExp = expression as UnaryExpression;
if (unaryExp != null)
memberExp = unaryExp.Operand as MemberExpression;
}
if (memberExp == null)
throw new ArgumentException("Cannot get name from expression", "expression");
return memberExp.Member.Name;
}
Update: From version 6.1 and onwards there is an [Index] attribute available.
For more info, see http://msdn.microsoft.com/en-US/data/jj591583#Index
This feature should be available in the near-future via data annotations and the Fluent API. Microsoft have added it into their public backlog:
http://entityframework.codeplex.com/workitem/list/basic?keywords=DevDiv [Id=87553]
Until then, you'll need to use a seed method on a custom Initializer class to execute the SQL to create the unique index, and if you're using code-first migrations, create a new migration for adding the unique index, and use the CreateIndex and DropIndex methods in your Up and Down methods for the migration to create and drop the index.
Check my answer here Entity Framework Code First Fluent Api: Adding Indexes to columns this allows you to define multi column indexes by using attributes on properties.
Okay, I'm really struggling with how to update a list of foreign keys in MVC2/EF4.
I have a one to many relationship between a Template object which can have many or no TemplateScenario objects.
Essentially, I have an edit method in a controller that is trying to do this:
// POST: /Modes/Edit/1
[HttpPost]
public ActionResult Edit(int id, FormCollection formValues)
{
Template template = _templateRepository.GetTemplate(id);
TemplateCreateViewModel viewModel = new TemplateCreateViewModel();
viewModel.Template = template;
viewModel.TemplateScenarioList = template.TemplateScenarios.ToList();
//Update the model
UpdateModel(viewModel);
UpdateModel(viewModel.Template.TemplateScenarios, "TemplateScenarioList", new[] { "ScenarioID", "TemplateID" });
_templateRepository.Save();
return RedirectToAction("Edit", new { id = template.TemplateID });
}
This code successfully updates the 'template' object. It also adds the 'templatescenario' child objects BUT only if it is the first time I have added 'templatescenarios' to this particular template. If any templatescenario objects already exist for a given template, and I try to update them based on the new list, I get this error:
"The operation failed: The relationship could not be changed because one or more
of the foreign-key properties is non-nullable. When a change is made to a
relationship, the related foreign-key property is set to a null value. If the
foreign-key does not support null values, a new relationship must be defined,
the foreign-key property must be assigned another non-null value, or the
unrelated object must be deleted."
The _templateRepository.Save(); is just calling the entities.SaveChanges() EF4 method.
I can solve this in a dirty way by passing down a list of templatescenario ids to my repository class in a custom 'update' method that looks like this:
public void Update(Template template, IList<int> templateScenarios)
{
//Delete Old Entries
foreach (TemplateScenario ts in entities.TemplateScenarios)
{
if (ts.TemplateID == template.TemplateID)
{
if (templateScenarios == null)
entities.TemplateScenarios.DeleteObject(ts);
else if (!templateScenarios.Where(tsl => tsl == ts.ScenarioID).Any())
entities.TemplateScenarios.DeleteObject(ts);
}
}
//Don't need to add anything if they are null.
if (templateScenarios == null)
return;
//Add New Entries
foreach (int ts in templateScenarios)
{
if (!entities.TemplateScenarios.Where(tsc => tsc.ScenarioID == ts && tsc.TemplateID == template.TemplateID).Any())
{
TemplateScenario tempScenToAdd = new TemplateScenario();
tempScenToAdd.ScenarioID = ts;
tempScenToAdd.TemplateID = template.TemplateID;
entities.TemplateScenarios.AddObject(tempScenToAdd);
}
}
}
But that just feels dirty and I think I'm so close with the first, more automatic method. I've scoured the internet and found some similar posts on stackoverflow but am finding it difficult to reach that 'aha' moment.
Thanks,
Tom.
Incidently, I sorted out my problem.
The problem was my joining table was incorrectly using it's own primary key instead of using a composite key based on two foreign keys. This is obviously wrong /bad practice and EF4 and UpdateModel() don't play nice.
I had inherited the DB design from an ex-collegue and thus had taken the db design as correct without thinking too much about it. Very stupid of me, I know.
I just spent the last 3-4 hours trying to retrieve a foreign key value using linq to entities and a stored procedure. Any advice is much appreciated.
public JsonResult GetEvents(double? start, double? end)
{
AnoEntities _dbAno = new AnoEntities();
var events = _dbAno.Events_GetByDateRange(fromDate, toDate);
var eventList = from e in events
select new
{
id = e.id,
title = e.title,
className = e.event_types.type.ToString()
};
return Json(eventList.ToArray());
}
type_id is the foreign key value that i'm trying to reach. I can't get it so appear in the entity data model and I can't seem to get to it. e.event_types and e.event_typesReference are both null so things like e.event_typesReference.EntityKey.EntityKeyValues.First().Value.ToString() aren't working.
Thanks!
I don't see any .Include methods or Load methods on even_types and I'm assuming your returning IEnumerable from your _dbAno.Events_GetByDateRange(fromDate, toDate). Like Craig pointed out in the comments if your return type of GetByDateRange is IQueryable you'd be projecting and EF should eager load for you.
Just a reminder that implicit lazy loading isn't supported out of the box in Entity Framework 1.0. You'll need to manually load the event_types with Load() or use the Include method on ObjectQuery.
I have an object that has been populated with the contents of four different related entities. However i have another entity in which i cannot include as part of the query due to it not being related in the navigation properites directly to the IQueryable table i am pulling. The entity i am trying to include is related to one of the four different entities that have been included successfully.
Is there a way to include(during db hit or afterwards) this entity as part of the overall object i am creating?
Here is an example of what my calls look like to build the CARTITEM object:
public List<CARTITEM> ListCartItem(Guid cartId)
{
//Create the Entity object
List<CARTITEM> itemInfo = null;
using (Entities webStoreContext = new Entities())
{
//Invoke the query
itemInfo = WebStoreDelegates.selectCartItems.Invoke(webStoreContext).ByCartID(cartId).ToList();
}
//Return the result set
return itemInfo;
}
here is the selectCartItems filter(Where i would normally do the includes):
public static Func<Entities, IQueryable<CARTITEM>> selectCartItems =
CompiledQuery.Compile<Entities, IQueryable<CARTITEM>>(
(cart) => from c in cart.CARTITEM.Include("ITEM").Include("SHIPPINGOPTION").Include("RELATEDITEM").Include("PROMOTION")
select c);
from this i have my CARTITEM object. Problem is i want to include the PROMOTIONTYPE table in this object, but since the CARTIEM entity doesn't have a navigation property directly to the PROMOTIONTYPE table i get an error.
Let me know if you need any more clarification.
Thanks,
Billy
You can use join and if it is the same database and server it should generate the join in SQL and do it all in one call...
LinqToEnties join example