As far as I can tell, EntityCollection.Attach and EntityReference.Attach can only create relationships that already exists in the database. In other words, if Address.EmployeeID == Employee.EmployeeID, then the following code will work:
Employee employee = context.Employees.First();
Address address = context.Addresses.First();
employee.Addresses.Attach(address);
But if Address.EmployeeID != Employee.EmployeeID, then the code will throw an exception:
Employee employee = context.Employees.First();
Address address = context.Addresses.First();
employee.Addresses.Attach(address); // System.InvalidOperationException: A
// referential integrity constraint
// violation occurred
But according to a code example taken from the following thread, EntityCollection.Attach and EntityReference.Attach can also be used to create a relationship that doesn't exist in a DB:
var existingPerson = ctx.Persons.SingleOrDefault(p => p.Name = "Joe Bloggs" };
var myAddress = ctx.Addresses.First(a => a.PersonID != existingPerson.PersonID);
existingPerson.Addresses.Attach(myAddress);
// OR:
myAddress.PersonReference.Attach(existingPerson)
ctx.SaveChanges();
So am I correct in assuming that EntityCollection.Attach and EntityReference.Attach can only create relationships that already exists in the database, and as such code example taken from the other thread should throw an exception?
Thank you
Yes, I think it's just a typing mistake or author has written something incomplete.
var existingPerson = ctx.Persons.SingleOrDefault(p => p.Name = "Joe Bloggs" };
var myAddress = ctx.Addresses.First(a => a.PersonID == existingPerson.PersonID);
existingPerson.Addresses.Attach(myAddress);
// OR:
myAddress.PersonReference.Attach(existingPerson)
ctx.SaveChanges();
Related
I did raw SQL query below to select only certain fields from a table.
{
List<CustEmpVM> CustomerVMlist = new List<CustEmpVM>();
var cid = db.Customers.SqlQuery("select SchedDate from Customer where CustID = '#id'").ToList<Customer>();
}
But i keep getting the error of:
System.Data.Entity.Core.EntityCommandExecutionException occurred in EntityFramework.SqlServer.dll but was not handled in user code
Additional information: The data reader is incompatible with the specified ALFHomeMovers.Customer. A member of the type, CustID, does not have a corresponding column in the data reader with the same name.
The exception message is pretty straightforward: the query expected to return full entity of Customer table but only SchedDate column returned, hence EF cannot done mapping other omitted columns including CustID.
Assuming Customers is a DbSet<Customer>, try return all fields from Customer instead:
// don't forget to include SqlParameter
var cid = db.Customers.SqlQuery("SELECT * FROM Customer WHERE CustID = #id",
new SqlParameter("id", "[customer_id]")).ToList();
If you want just returning SchedDate column, materialize query results and use Select afterwards:
var cid = db.Customers.SqlQuery("SELECT * FROM Customer WHERE CustID = #id",
new SqlParameter("id", "[customer_id]"))
.AsEnumerable().Select(x => x.SchedDate).ToList();
NB: I think you can construct LINQ based from the SELECT query above:
var cid = (from c in db.Customers
where c.CustID == "[customer_id]"
select c.SchedDate).ToList();
Similar issue:
The data reader is incompatible with the specified Entity Framework
Use below query instead of raw query:
{
List<CustEmpVM> CustomerVMlist = new List<CustEmpVM>();
var cid = db.Customers.Where(w=>w.Id == YOURCUSTOMERID).Select(s=>new Customer{SchedDate = s.SchedDate }).ToList();
}
It will give compile time error rather than run time error.
I am trying to implement simple membership in my application. My problem is that I want to be able to display the data in the userprofile table for the current user but I dont know how to select it from the DB
I have tried this but I am getting an error:
UserProfile UserP = new UserProfile();
ViewBag.Message = User.Identity.Name;
return View();
UserP = (from r in up.UserName
where up.UserName == User.Identity.Name.ToString()
select r).ToList().FirstOrDefault();
return View(UserP);
Here is the error:
Error 1 Cannot implicitly convert type 'char' to 'MvcApplication5.Models.UserProfile' C:\Users\user\Desktop\MvcApplication5\MvcApplication5\Controllers\HomeController.cs 31 32 MvcApplication5
If I got you right (your code is little bit broken, it has two returns, so I assume there is just two pieces of code), try this:
UserP = (from r in up
where up.UserName == User.Identity.Name.ToString()
select r).FirstOrDefault();
Just get rid of up.UserName in your query. ToList() is also not needed.
P.S. For the future:
I also suggest you adding another column called LoweredUserName and perform checking in the following way:
where up.LoweredUserName == User.Identity.Name.ToString().ToLower()
Here is how you can access the UserProfile.
var context = new UsersContext();
var username = User.Identity.Name;
var user = context.UserProfiles.SingleOrDefault(u => u.UserName == username);
return View(user);
For more on customizing the UserProfile and accessing it read this article.
Few days back I put a question regarding mapping two classes Message and MessageStatusHistory using EF. The mapping is going fine but I am facing some problems with the navigation property StatusHistory in class Message that relates it to MessageStatusHistory objects. I am loading the messages for one user only and want to the statuses pertaining to that user only. Like I would want to show if the user has marked message as read/not-read and when. If I use default loading mechanism like following it loads all the history related to the message irrespective of the user:
IDbSet<Message> dbs = _repo.DbSet;
dbs.Include("StatusHistory").Where(x=>x.MessageIdentifier == msgIdentifier);
To filter history for one user only I tried following trick:
IDbSet<Message> dbs = _repo.DbSet;
var q = from m in dbs.Include("StatusHistory")
where m.MessageIdentifier == msgIdentifier
select new Message
{
MessageIdentifier = m.MessageIdentifier,
/*OTHER PROPERTIES*/
StatusHistory = m.StatusHistory
.Where(x => x.UserId == userId).ToList()
};
return q.ToList();//THROWING ERROR ON THIS LINE
I am getting the error:
The entity or complex type 'MyLib.Biz.Message' cannot be constructed in a LINQ
to Entities query.
I have tried by commenting StatusHistory = m.StatusHistory.Where(x => x.UserId == userId).ToList() also but it has not helped.
Please help me in getting Messages with filtered StatusHistory.
EDIT:- above is resolved with this code:
var q = from m in _repository.DBSet.Include("Histories")
where m.MessageIdentifier == id
select new {
m.Id,/*OTHER PROPERTIES*/
Histories = m.Histories.Where(x =>
x.SenderId == userId).ToList()
};
var lst = q.ToList();
return lst.Select(m => new Message{
Id = m.Id, MessageIdentifier = m.MessageIdentifier,
MessageText = m.MessageText, Replies = m.Replies,
ReplyTo = m.ReplyTo, Histories = m.Histories, SenderId =
m.SenderId, SenderName = m.SenderName, CreatedOn = m.CreatedOn
}).ToList();
But if I try to include replies to the message with:
from m in _repository.DBSet.Include("Replies").Include("Histories")
I am getting error on converting query to List with q.ToList() for Histories = m.Histories.Where(x=> x.SenderId == userId).ToList().
About your EDIT part: You cannot use ToList() in a projection, just leave it an IEnumerable<T> and convert to a List<T> when you construct the Message. You also don't need to create two list objects, you can switch from the LINQ to Entities query to LINQ to Objects (the second Select) by using AsEnumerable():
var list = (from m in _repository.DBSet
where m.MessageIdentifier == id
select new {
// ...
Histories = m.Histories.Where(x => x.SenderId == userId)
})
.AsEnumerable() // database query is executed here
.Select(m => new Message {
// ...
Histories = m.Histories.ToList(),
// ...
}).ToList();
return list;
Be aware that Include has no effect when you use a projection with select. You need to make the properties that you want to include part of the projection - as you already did with select new { Histories.....
Some pseudo-code of the model I'm working with:
User { int Id, string Username }
Activity { int Id, string Name }
Place { int Id, string Name }
Basically I have a bunch of Users and they belong to certain places (many to many relationship in RDBMS world). What I'd like to do now that I've created all of the nodes already is create the relationship between them. To do that I believe I need to get references to each node and then simply create the relationship between them.
Note: So far no relationships exist. It does look like in some of the examples they have added the User nodes with a relationship that points to the RootNode but I have no idea why. I'm not sure if I need to do that or not.
More pseudo-code:
var userRef = _graphClient...GetUserNodeWhereIdEquals(user.Id);
// or something like _graphClient.OutV<User>("[[id={0}]]", user.Id)
// or even just _graphClient.V<User>(id == user.Id)
var placeRef = _graphClient...GetPlaceNodeWhereIdEquals(place.Id);
_graphClient...CreateRelationshipBetween(userRef, placeRef, "belongs_to");
Unfortunately the documentation starts off pretty great then goes south when you get to relationships.
Update 3/29/12
Here's the code I have so far:
foreach (var a in _activityTasks.GetAll())
{
_graphClient.Create(a, new ActivityBelongsTo(_graphClient.RootNode));
}
foreach (var p in _placeTasks.GetAll().Take(1))
{
var placeNode = _graphClient.Create(p, new PlaceBelongsTo(_graphClient.RootNode));
foreach (var activity in p.Activities)
{
Activity activity1 = activity;
var activityNode = _graphClient.RootNode.In<Activity>(ActivityBelongsTo.TypeKey, a => a.Id == activity1.Id).SingleOrDefault();
_graphClient.CreateRelationship(placeNode, new PlaceHasActivity(activityNode.Reference));
}
}
The activity nodes are created fine. The place node is created fine. An error is now being thrown when trying to get the activityNode. It's a rather large stack trace so I'll try to paraphrase here:
Received an exception when executing the request.
The query was: g.v(p0).in(p1).filter{ it[p2] == p3
}.drop(p4).take(p5)._()
The exception was: Value cannot be null. Parameter name: key
System.ArgumentNullException: Value cannot be null.Parameter name: key
at System.Collections.Generic.Dictionary`2.Insert(TKey key, TValue
value, Boolean add) ... The raw response body was: [ {
"outgoing_relationships" :
"http://localhost:7474/db/data/node/2/relationships/out", "data" : {
"Name" : "Aerobics", "Id" : 2 }, "all_typed_relationships" :
"http://localhost:7474/db/data/node/2/relationships/all/{-list|&|types}",
"traverse" :
"http://localhost:7474/db/data/node/2/traverse/{returnType}", "self"
: "http://localhost:7474/db/data/node/2", "property" :
"http://localhost:7474/db/data/node/2/properties/{key}",
"outgoing_typed_relationships" :
"http://localhost:7474/db/data/node/2/relationships/out/{-list|&|types}",
"properties" : "http://localhost:7474/db/data/node/2/properties",
"incoming_relationships" :
"http://localhost:7474/db/data/node/2/relationships/in", "extensions"
: { }, "create_relationship" :
"http://localhost:7474/db/data/node/2/relationships",
"paged_traverse" :
"http://localhost:7474/db/data/node/2/paged/traverse/{returnType}{?pageSize,leaseTime}",
"all_relationships" :
"http://localhost:7474/db/data/node/2/relationships/all",
"incoming_typed_relationships" :
"http://localhost:7474/db/data/node/2/relationships/in/{-list|&|types}"
} ]
Something to do when adding a item to a Dictionary when the key is null. Problem is, I don't see any nulls when I debug on my end, activity1 is there, RootNode is there, TypeKey is a const string.
I'm almost wondering if I should just keep the created nodes within a array or Dictionary myself and then just working with the NodeReference. That's what I'm going to try next.
Later that morning
This seems to load everything into the graph database fine:
var activityNodes = _activityTasks.GetAll().ToDictionary(a => a.Id, a => _graphClient.Create(a, new ActivityBelongsTo(_graphClient.RootNode)));
foreach (var p in _placeTasks.GetAll())
{
var placeNode = _graphClient.Create(p, new PlaceBelongsTo(_graphClient.RootNode));
foreach (var activity in p.Activities)
{
_graphClient.CreateRelationship(placeNode, new PlaceHasActivity(activityNodes[activity.Id]));
}
}
foreach (var u in _userTasks.GetAllUserGraph())
{
var userNode = _graphClient.Create(u, new UserBelongsTo(_graphClient.RootNode));
foreach(var activity in u.Activities)
{
_graphClient.CreateRelationship(userNode, new UserParticipatesIn(activityNodes[activity.Id]));
}
}
Now the problem is similar to what I had before. Now I want to get an activity that has a relationship to the RootNode:
Node<Activity> activity = _graphClient
.RootNode
.In<Activity>(ActivityBelongsTo.TypeKey, a => a.Id == 1)
.SingleOrDefault();
Throwing the key value can't be null exception again. I think I need to investigate the gremlin syntax more. I'm guessing the problem is there.
This afternoon
Started to experiment with Gremlin queries:
g.v(0).inE.filter{it.label=="ACTIVITY_BELONGS_TO"}.outV.filter{it.Id==1}.Name
works fine. I tried to replicate that using neo4jClient syntax:
_graphClient.RootNode.InE(ActivityBelongsTo.TypeKey).OutV(b => b.Id == 1).SingleOrDefault();
Same null exception, it spits out:
g.v(p0).inE.filter{ it[p1].equals(p2) }.outV.filter{ it[p3] == p4 }.drop(p5).take(p6)._()
which looks right to me, except for the end. Ran this though:
g.v(0).inE.filter{it.label=="ACTIVITY_BELONGS_TO"}.outV.filter{it.Id==1}.drop(0).take(1)._()
And that works fine. Something stinks here...maybe I should try the other library although I liked the de/serialization support. Sigh...
Thought maybe a raw query would work. Nope! This method no longer accepts a string and the required GremlinQuery I have no idea how to you. Grooooooooooooooooan.
var users = graphClient.ExecuteGetAllNodesGremlin<IsCustomer>("g.v(0).out('IsCustomer'){it.'Name' == 'BobTheBuilder'}");
Update 3/30/12
Created a new project, everything below works fine. Super confused why it will work here... :( Maybe version differences, I have no idea.
var client = new GraphClient(new Uri("http://localhost:7474/db/data"));
client.Connect();
client.Create(new User { Id = 1, Username = "joe" }, new UserBelongsTo(client.RootNode));
client.Create(new User { Id = 2, Username = "cloe" }, new UserBelongsTo(client.RootNode));
client.Create(new Activity { Id = 1, Name = "Bocce Ball" }, new ActivityBelongsTo(client.RootNode));
client.Create(new Activity { Id = 2, Name = "Programming" }, new ActivityBelongsTo(client.RootNode));
var user = client.RootNode.In<User>(UserBelongsTo.TypeKey, u=>u.Id == 1).SingleOrDefault();
var activity = client.RootNode.In<Activity>(ActivityBelongsTo.TypeKey, a=>a.Id == 1).SingleOrDefault();
client.CreateRelationship(user.Reference, new Plays(activity.Reference));
user = client.RootNode.In<User>(UserBelongsTo.TypeKey, u => u.Id == 1).SingleOrDefault();
activity = client.RootNode.In<Activity>(ActivityBelongsTo.TypeKey, a => a.Id == 1).SingleOrDefault();
I'm just getting started too. I would suggest you check out this blog:
http://romikoderbynew.com/2011/07/30/neo4jclient-primer/
Also, check http://frictionfree.org and its source code (in the about section) for more examples.
Creating relationships on existing - as I understand, this is possible. However, it appears to be easier to associate nodes as you create them. From the blog:
You can also create relationships between existing nodes.
graphClient.CreateRelationship(customerNodeReference, new
Speaks(languageNode.Reference));
RootNode - I believe you need to start a query from a node, I don't think you can do a
SELECT * FROM ... WHERE
Therefore, it would make sense that you need to attach nodes to the root node. This is an example from the FrictionFreeApp:
var node = graphClient.Create(
user,
new UserBelongsTo(rootNode));
I want to create a new row in my database on a table that has a couple of foreign key relationships and I haven't been able to get a handle on what order and what calls need to be made. This is what I have so far:
db.Models.Order order = DB.Models.Order.CreateOrder( apple );
order.CustomerReference.Attach( ( from c in db.Customer where c.Id == custId select c ).First() );
db.SaveChanges();
The code is failing on the second line there, saying:
Attach is not a valid operation when
the source object associated with this
related end is in an added, deleted,
or detached state. Objects loaded
using the NoTracking merge option are
always detached.
Any ideas?
(Thanks John for the grammar fixes)
So I figured it out. This is what you have to do:
db.Models.Order order = DB.Models.Order.CreateOrder( apple );
order.Customer = (from c in db.Customer where c.Id == custId select c).First();
db.SaveChanges();
I hope that helps people.
Why not use entity references? Your method will cause an extra SELECT statement.
A much nicer way is to use the CustomerReference class and an EntityKey.
order.CustomerReference = new System.Data.Objects.DataClasses.EntityReference<Customers>();
order.CustomerReference.EntityKey = new EntityKey("ModelsEntities.Customers", "Id", custId);
For update here is some sample code:
using (var ctx = new DataModelEntities())
{
var result = (from p in ctx.UserRole.Where(o => o.UserRoleId == userRole.UserRoleId)
select p).First();
result.RolesReference.EntityKey = new EntityKey("DataModelEntities.Roles",
"RoleId", userRole.RoleId);
result.UserRoleDescription = userRole.UserRoleDescription;
ctx.SaveChanges();
}