We Keep Coding

Select Entity property in related table using linq

here is my setup.
Base Model
public class Base
{
public int BaseID { get; set; }
[StringLength(8)]
[Index(IsUnique = true)]
public string BaseNumber { get; set; }
public ICollection<BillOfMaterial> billOfMaterials { get; set; }
}
BillOfMaterial Model
public class BillOfMaterial
{
public int BillOfMaterialID { get; set; }
[StringLength(10)]
[Index(IsUnique = true)]
public string BomNumber { get; set; }
public ICollection<Base> Bases { get; set; }
}
What I am trying to do is select all bill of material BomNumbers where the base is equal to a input base number.
What I have tried
BaseNumber = "A1C1D001";
var BOMQuery = (from Base in db.Bases.Include("BillOfMaterials")
where Base.BaseNumber == BaseNumber
select Base.billOfMaterials.ToList());
When trying to create this query I can't see the BomNumber property when I do => select Base.BillOfMaterials.(Can't Find Property)
I tried using the .Include() extension to try and bring in the related table in hopes it would give me the property. Not sure how to word this question exactly to do a good google search for the answer. What am I doing wrong here? Any help would be appreciated.
Thank you,

When you only need a list of BOMs use the following:
var BOMQuery = db.Bases
.Where(x => x.BaseNumber == BaseNumber)
.SelectMany(a => a.billOfMaterials.Select(b => b.BomNumber)).ToList();
You can then add it to an ObservableCollection like this:
BomList = new ObservableCollection<string>(BOMQuery);

Can't insert entity with foreign key in Entity Framework

I'm building Backend for Mobile Application with ASP.NET MVC Framework.
I have two Objects:
public class CarLogItem : EntityData
{
public CarLogItem(): base()
{
Time = DateTime.Now;
}
public DateTime Time { get; set; }
public int RPM { get; set; }
public int Speed { get; set; }
public int RunTime { get; set; }
public int Distance { get; set; }
public int Throttle { get; set; }
[ForeignKey("Trip")]
public String Trip_id { get; set; }
// Navigation property
public TripItem Trip { get; set; }
}
and
public class TripItem : EntityData
{
public TripItem() : base()
{
UserId = User.GetUserSid();
StartTime = DateTime.Now;
logItems = new List<CarLogItem>();
}
public string UserId { get; set; }
public List<CarLogItem> logItems {get;set;}
public DateTime StartTime { get; set; }
}
and I have controller, which add new CarLogItem to database.
public class CarLogItemController : TableController<CarLogItem>
{
// POST tables/CarLogItem
public async Task<IHttpActionResult> PostCarLogItem(CarLogItem item)
{
var lastItem = db.CarLogItems.OrderByDescending(x => x.Time).FirstOrDefault();
//lastItem = (Query().Where(logitem => true).OrderBy(logitem => logitem.Time)).Last();
//checking if lastItem.Trip isn't null because
// I have entities with Trip field is null, but all of them should have it.
if (lastItem != null && lastItem.Trip != null && item.RunTime > lastItem.RunTime)
{
item.Trip = lastItem.Trip;
}
//In order to test adding of new TripItem entity to database
// I compare item.RunTime with 120, so it always true
else if (lastItem == null || item.RunTime < 120) // < lastItem.RunTime)
{
var newTrip = new TripItem();
item.Trip = newTrip;
}
else
{
throw new ArgumentException();
}
CarLogItem current = await InsertAsync(item);
return CreatedAtRoute("Tables", new { id = current.Id }, current);
}
}
When I'm trying to add new CarLogItem with Trip = null it's ok, but when Trip is particular object it fails with following Exception:
The entity submitted was invalid: Validation error on property 'Id': The Id field is required
How properly to add new CarLogItem with nested TripItem?

I think that you need to populate the Id property on your TripItem, e.g.
var newTrip = new TripItem(){ Id = Guid.NewGuid() }

You need a primary key field in every entity class, like Id or CarLogItemId (ClassName + "Id"). Or just have a property with [Key] attribute:
[Key]
public string/int/Guid/any-db-supported-type MyProp { get; set; }
Entity Framework relies on every entity having a key value that it
uses for tracking entities. One of the conventions that code first
depends on is how it implies which property is the key in each of the
code first classes. That convention is to look for a property named
“Id” or one that combines the class name and “Id”, such as “BlogId”.
The property will map to a primary key column in the database.
Please see this for more details.
I also suspect this to be a problem:
public Lazy<CarLogItem> logItems { get; set; }
You don't have to mark navigation property as Lazy<>. It is already lazy (unless you have configuration that disables lazy loading). Please try to remove Lazy<> and see if it works this way.

Dynamically add a linked field to an ASP.NET MVC EF model

I have the following database table:
ID ParentID LinksTo
---------------------
0 null "1,2"
1 0 "0,2"
2 0 "1"
It's a hierarchical design, where each records points to a parent record from the same table. I know the LinksTo field is a very bad design, but the table is given, I cannot change that. (Note that the LinksTo field creates a sort of many-to-many relationship.)
Using Code-First EF, I have the following model class:
public class Item
{
public int ID { get; set; }
public int ParentID { get; set; }
public string LinksTo { get; set; }
public virtual Item Parent { get; set; }
[InverseProperty("Parent")]
public virtual ICollection<Item> Children { get; set; }
}
Now, how can I add a dynamic property to the model so that I can access the Item collections Item.LinksTo and Item.LinksFrom (the reverse) in code?

I guess I'd do something like this:
private List<Item> _linkedItems;
private void UpdateLinksTo() {
this.LinksTo = string.Join<string>(_linkedItems.Select(i => i.ID.ToString()));
}
[NotMapped]
public ReadOnlyCollection<Item> LinkedItems {
get {
if(_linkedItems == null) {
_linkedItems = db.Items.Where(i => this.LinksTo.Split(',').Select(x => int.Parse(x)).Contains(i.ID)).ToList();
}
return _linkedItems.AsReadOnly();
}
}
[NotMapped]
public void AddLinkedItem(Item item) {
if(!_linkedItems.Select(i => i.ID).Contains(item.ID)) {
_linkedItems.Add(item);
UpdateLinksTo();
}
}
That will give you access to a read-only collection with methods to alter it (you can also make a DeleteLinkedItem method) which is about as good as you're going to do I think.
I haven't checked to even see if this compiles, btw.

Entity Framework using Load with Select - is it possible?

I'm trying to optimize my EF queries and I'm stuck with this one.
Let's say I have a model like this:
public class House
{
public int ID { get; set; }
public ICollection<Window> Windows { get; set; }
}
public class Window
{
public int ID { get; set; }
public string Color { get; set; }
public WindowKind Kind { get; set; }
}
public class WindowKind
{
public int ID { get; set; }
public string Name { get; set; }
public string Description { get; set; }
}
What I would like to do is to explicitly load all windows and to specify what should be populated in WindowKind property.
I know I can do it with .Include() like this:
var house = Context.Houses.Single(h => h.ID == id);
var windows = Context.Entry(house).Collection(h => h.Windows).Query().Include(w => w.Kind).Load();
However, this will create a query that will load all WindowKind properties and I need only Name, for example. I was hoping something like this would work but it does not, Windows collection is empty, although the generated query looks good.
var house = Context.Houses.Single(h => h.ID = id);
var windows = Context.Entry(house).Collection(h => h.Windows).Query().Select(w => { new w.Color, w.Kind.Name }).Load();
Is it possible to have fine grained control when loading child collections?

you can't load only a part of the scalar (int, string,...) properties of an entity by loading the entity.
In you case, something like the following should do:
from
w in Context.Windows
where
w.House.ID == id // here a navigation property is missing, but (imho) more clear for the sample
select new {
windows = w,
kName = w.Kind.Name
}
But in this case you will not get context attached entities.

Database items getting deleted when referencing them multiple times

I am creating a simple blogging application to get .NET MVC 4 down and I am having a problem. Everything works except for when I try to tag a blog using an array of strings for each blog like so:
public class BlogEntry
{
public List<Comment> BlogComments { get; set; }
public virtual List<String> RawTags { get; set; }
public virtual List<Tag> BlogTags { get; set; }
public virtual User Author { get; set; }
public int AuthorId { get; set; }
public string Title { get; set; }
public string Content { get; set; }
public DateTime DatePosted { get; set; }
[Key]
public int Id { get; set; }
public bool IsAcceptingComments { get; set; }
public bool IsVisible { get; set; }
public DateTime LastEdited { get; set; }
}
public class Tag
{
[Key]
public int Id { get; set; }
public string Name { get; set; }
public int RefCount { get; set; }
}
Upon creating a blog and tagging it, I save tags into the BlogEntry model using this:
[HttpPost]
public int Create(string data)
{
if (data != null)
{
BlogEntry newBlog = JsonConvert.DeserializeObject<BlogEntry>(data);
newBlog.Author = Session["user"] as User;
newBlog.AuthorId = newBlog.Author.Id;
newBlog.IsVisible = true;
newBlog.IsAcceptingComments = true;
newBlog.LastEdited = DateTime.Now;
newBlog.DatePosted = DateTime.Now;
newBlog.BlogTags = new List<Tag>();
foreach (String s in newBlog.RawTags)
{
// First check to see if the tag already exists
Tag check = Db.Tags.Where(m => m.Name == s).FirstOrDefault();
if (check != null)
{
check.RefCount++;
newBlog.BlogTags.Add(check);
Db.Tags.Attach(check);
Db.Entry(check).State = System.Data.Entity.EntityState.Modified;
Db.SaveChanges();
}
else
{
// Create a new tag
Tag newTag = new Tag();
newTag.Name = s;
newTag.RefCount = 1;
newBlog.BlogTags.Add(newTag);
Db.Tags.Add(newTag);
}
}
Db.BlogEntries.Add(newBlog);
Db.SaveChanges();
return newBlog.Id;
}
return -1;
}
First I do a check to see if a tag already exists.. If it does, I try to add the same tag, check to the newBlog object. I would have thought that this would just save a reference to this Tag object in the DbSet, however, if I create multiple blogs posts with the tag "html" and then run a query to see what blogs have the html tag, only the most recently tagged blog retains this value.... What can I do so that I can have multiple BlogEntry objects with the same Tag object in the database?

I don't have my dev machine in front of me right now, so this is just a guess, but I figure it's better than making you wait until tomorrow...
I don't think you need the last 3 lines in your if(check!=null) and in fact, I wonder if they aren't messing you up:
Db.Tags.Attach(check);
Db.Entry(check).State = System.Data.Entity.EntityState.Modified;
Db.SaveChanges();
You shouldn't need to attach because you got it from the Db object already, so it should already be being tracked. This means you don't need to change the state and as for the SaveChanges, you are going to do that below.
And now another disclaimer: I've done some work with Entity Framework (version 6, if you want to know), but not with MVC, so it may be different, but my understanding is that it is better to create a new DbContext for each set of instructions, rather than having a class variable that just tracks running changes. I'm not sure if that is what you are doing or not, but it sort of looks that way from this code sample. Assuming that is relevant in MVC, you may consider creating a new DbContext (Db) at the top of your create method.
Let me know how it goes--if this doesn't help, I'll delete this answer.

First you would have to update the Tag class so that it can track its registered blog entries itself. Here the BlogEntry and Tag classes have a many-to-many relationship. So the Tag class would look like below:
public class Tag
{
[Key]
public int Id { get; set; }
public string Name { get; set; }
public int RefCount { get; set; }
public virtual List<BlogEntry> BlogEntries { get; set; } // MODIFICATION
}
Now you have to add the blog entry to all of its tags for back referencing to meet your query in an easy way. Look for the modifications I have made in the for-loop below:
foreach (String s in newBlog.RawTags)
{
// First check to see if the tag already exists
Tag check = Db.Tags.Where(m => m.Name == s).FirstOrDefault();
if (check != null)
{
check.RefCount++;
check.BlogEntries.Add(newBlog); // MODIFICATION
newBlog.BlogTags.Add(check);
Db.Tags.Attach(check);
Db.Entry(check).State = System.Data.Entity.EntityState.Modified;
Db.SaveChanges();
}
else
{
// Create a new tag
Tag newTag = new Tag();
newTag.Name = s;
newTag.RefCount = 1;
newTag.BlogEntries = new List<BlogEntry>(); // MODIFICATION
newTag.BlogEntries.Add(newBlog); // MODIFICATION
newBlog.BlogTags.Add(newTag);
Db.Tags.Add(newTag);
}
}
To see what blogs have the html tag, you just have to query on the Tag class and search through the BlogEntries to get the desired blogs. Good luck!