I was planning to use EntityFramework-Plus for bulk operations however i am not sure if it supports bulk insert.
So for example, i have Parent entities and i want to insert Child entities in bulk how do i dot that using EF Plus
In code below number of parents could be between 1000-2000 range and number of children are 10-20. I want to add same children for each parent, if condition satisfies
public async Task AddChildern(IEnumerable<Child> children)
{
var ids = GetIDs();
var result = _dbContext.Parent.Where(x=> ids.contains(x.ID)).ToListAsync();
foreach(var p in result)
{
foreach(var child in children)
{
var flag = CanAddChild(child);
if(flag)
{
p.Children.Add(child);
}
}
}
}
Disclaimer: I'm the owner of the project Entity Framework Plus
This library doesn't support BulkInsert.
Disclaimer: I'm the owner of the project Entity Framework Extensions
This library supports BulkInsert but it's not free.
(EF Plus is powered by this library)
In your scenario, since it looks child entity doesn't have a direct relation to the parent (No navigation property or parent ID), you should use the BulkSaveChanges method.
public async Task AddChildern(IEnumerable<Child> children)
{
var ids = GetIDs();
var result = _dbContext.Parent.Where(x=> ids.contains(x.ID)).ToListAsync();
foreach(var p in result)
{
foreach(var child in children)
{
var flag = CanAddChild(child);
if(flag)
{
p.Children.Add(child);
}
}
}
}
// ...code...
_dbContext.BulkSaveChanges();
EDIT: Answer Comment
Child does have ParentID
Depending on how the relation is set, you could also do a direct BulkInsert.
_dbContext.BulkInsert(result.SelectMany(x => x.Children));
I need to map EF entities to respective DTO. In the example below I have EF entities Parent and Child, and Child entity contains reference to Parent object. I also have ParentDto and ChildDto (DTO), and ChildDto contains reference to ParentDto (not Parent). So, how can I assign ParentDto reference to ChildDto instance in below method:
public Task<List<ParentDto>> Method()
{
return (Context.Set<Parent>()
.Where(someCondition)
.Select(p => new ParentDto
{
// here we map all properties from Parent to ParentDto
... ,
Children = p.Children.Select(c => new ChildDto
{
// here we map all properties from Child to ChildDto
... ,
Parent = ? // reference to newly created ParentDto instance
})
}).ToListAsync();
}
You have to use a variable but you can't do it in a lambda expression. You have to do the mapping in memory after calling ToListAsync():
public Task<List<ParentDto>> Method()
{
var parents = await (Context.Set<Parent>()
.Where(someCondition)
.ToListAsync());
return parents.Select(p =>
{
var parent = new ParentDto();
//map parent properties
parent.Children = p.Children.Select(c => new ChildrenDto
{
//map child properties
});
return parent;
}).ToList();
}
In regular LINQ (not to entities) this isn't possible because of an important feature of object initializers: atomic assignment. As you can read here, an object initialization like...
var c = new Customer() { Name = "Bart", City = "Redmond", Age = 24 };
...is equivalent to...
Customer __t = new Customer();
__t.Name = "Bart";
__t.City = "Redmond";
__t.Age = 24;
Customer c = __t;
So the object is created and fully initialized first and then its reference is exposed. Therefore, if inside the object another object is initialized, the nested object will never be able to grab a reference to its parent during the initialization phase. You can only assign the parent afterwards.
Although in LINQ-to-entities the mechanism of creating objects is entirely different, the initialization logic can be considered identical, and the same restrictions apply.
As you know, in LINQ-to-Entities we can't call instance methods of entities while we're in the query expression. Else you could, for instance, have called some method in Parent that constructs its children (and assigns itself to it as their parent). As it is now, the only thing you can do is construct the Parents with their nested parent.Children first and after that, traverse the parent.Children collections and assign their Parent to them (as in Ufuk's answer).
I am using Breeze.js with Entity Framework WebAPI backend, and I need to delete a large set of data that is not loaded to client. I would really like to do it on the server and not load it.
Is there a "breeze way"? By that I mean a method in a BreezeController.
EDIT
I have to delete all rows from one table that belong to the user, whose date field is in future, and all their child rows.
public override int SaveChanges()
{
foreach (
var entry in
this.ChangeTracker.Entries()
.Where((e => (e.State == (EntityState) Breeze.WebApi.EntityState.Deleted))))
{
if (entry.Entity.GetType() == typeof(User))
{
var entity = entry.Entity as User;
var childEntitiesInFuture = ChildEntities.Where(c => c.DateField > DateTime.Now);
foreach (var child in childEntitiesInFuture){
var grandchildrenForDeletion = Grandchildren.Where(c => c.ChildId == child.Id);
foreach (var g in grandchildrenForDeletion) Grandchildren.Remove(g);
ChildEntities.Remove(child);
}
}
}
}
Assuming you are deleting User, one User has many ChildEntity saved in ChildEntities and each ChildEntity has many Grandchild saved in Grandchildren. A bit messy names, but that's what you get with no real names :)
This method goes into your Context class. Good luck.
I have loaded my product catalog using Entity Framework
I would like to iterate all items to find a specific item
the structure is
Category -> [Subcategory ->] Product -> options
Subcategory, product and options are EntityCollection of their specific type
All types derive from EntityObject
Let's say I'm looking for option 12 but I don't know in which product it is in.
How can I iterate all objects to find the option 12 ? I have this so far. in my EntityObject, I know it's not recursive yet but will eventually be once i know which properties are collections, I might be approaching it the wrong way ...
public T Find<T>(Type type, int id) where T : EntityObject
{
//get all properties
PropertyInfo[] properties = this.GetType().GetProperties();
// foreach property find the one
foreach (PropertyInfo oPropertyInfo in properties)
{
// check for type
if (oPropertyInfo.PropertyType == type)
{
PersistentEntity o = oPropertyInfo.GetValue(this, null) as EntityObject;
if (o != null && o.Id == id)
{
return (T)o;
}
}
// if property has childs, is IEnumerable -> recursive
}
return (T)new EntityObject();
}
How about this?
var query =
from c in categories
from sc in c.SubCategories
from from p in sc.Products
from o in p.Options
where o.Id == 2
select c /* or p?? */;
I have a tree structure in the DB with TreeNodes table. the table has nodeId, parentId and parameterId. in the EF, The structure is like TreeNode.Children where each child is a TreeNode...
I also have a Tree table with contain id,name and rootNodeId.
At the end of the day I would like to load the tree into a TreeView but I can't figure how to load it all at once.
I tried:
var trees = from t in context.TreeSet.Include("Root").Include("Root.Children").Include("Root.Children.Parameter")
.Include("Root.Children.Children")
where t.ID == id
select t;
This will get me the the first 2 generations but not more.
How do I load the entire tree with all generations and the additional data?
I had this problem recently and stumbled across this question after I figured a simple way to achieve results. I provided an edit to Craig's answer providing a 4th method, but the powers-that-be decided it should be another answer. That's fine with me :)
My original question / answer can be found here.
This works so long as your items in the table all know which tree they belong to (which in your case it looks like they do: t.ID). That said, it's not clear what entities you really have in play, but even if you've got more than one, you must have a FK in the entity Children if that's not a TreeSet
Basically, just don't use Include():
var query = from t in context.TreeSet
where t.ID == id
select t;
// if TreeSet.Children is a different entity:
var query = from c in context.TreeSetChildren
// guessing the FK property TreeSetID
where c.TreeSetID == id
select c;
This will bring back ALL the items for the tree and put them all in the root of the collection. At this point, your result set will look like this:
-- Item1
-- Item2
-- Item3
-- Item4
-- Item5
-- Item2
-- Item3
-- Item5
Since you probably want your entities coming out of EF only hierarchically, this isn't what you want, right?
.. then, exclude descendants present at the root level:
Fortunately, because you have navigation properties in your model, the child entity collections will still be populated as you can see by the illustration of the result set above. By manually iterating over the result set with a foreach() loop, and adding those root items to a new List<TreeSet>(), you will now have a list with root elements and all descendants properly nested.
If your trees get large and performance is a concern, you can sort your return set ASCENDING by ParentID (it's Nullable, right?) so that all the root items are first. Iterate and add as before, but break from the loop once you get to one that is not null.
var subset = query
// execute the query against the DB
.ToList()
// filter out non-root-items
.Where(x => !x.ParentId.HasValue);
And now subset will look like this:
-- Item1
-- Item2
-- Item3
-- Item4
-- Item5
About Craig's solutions:
You really don't want to use lazy loading for this!! A design built around the necessity for n+1 querying will be a major performance sucker. ********* (Well, to be fair, if you're going to allow a user to selectively drill down the tree, then it could be appropriate. Just don't use lazy loading for getting them all up-front!!)I've never tried the nested set stuff, and I wouldn't suggest hacking EF configuration to make this work either, given there is a far easier solution. Another reasonable suggestion is creating a database view that provides the self-linking, then map that view to an intermediary join/link/m2m table. Personally, I found this solution to be more complicated than necessary, but it probably has its uses.
When you use Include(), you are asking the Entity Framework to translate your query into SQL. So think: How would you write an SQL statement which returns a tree of an arbitrary depth?
Answer: Unless you are using specific hierarchy features of your database server (which are not SQL standard, but supported by some servers, such as SQL Server 2008, though not by its Entity Framework provider), you wouldn't. The usual way to handle trees of arbitrary depth in SQL is to use the nested sets model rather than the parent ID model.
Therefore, there are three ways which you can use to solve this problem:
Use the nested sets model. This requires changing your metadata.
Use SQL Server's hierarchy features, and hack the Entity Framework into understanding them (tricky, but this technique might work). Again, you'll need to change your metadata.i
Use explicit loading or EF 4's lazy loading instead of eager loading. This will result in many database queries instead of one.
I wanted to post up my answer since the others didn't help me.
My database is a little different, basically my table has an ID and a ParentID. The table is recursive. The following code gets all children and nests them into a final list.
public IEnumerable<Models.MCMessageCenterThread> GetAllMessageCenterThreads(int msgCtrId)
{
var z = Db.MCMessageThreads.Where(t => t.ID == msgCtrId)
.Select(t => new MCMessageCenterThread
{
Id = t.ID,
ParentId = t.ParentID ?? 0,
Title = t.Title,
Body = t.Body
}).ToList();
foreach (var t in z)
{
t.Children = GetChildrenByParentId(t.Id);
}
return z;
}
private IEnumerable<MCMessageCenterThread> GetChildrenByParentId(int parentId)
{
var children = new List<MCMessageCenterThread>();
var threads = Db.MCMessageThreads.Where(x => x.ParentID == parentId);
foreach (var t in threads)
{
var thread = new MCMessageCenterThread
{
Id = t.ID,
ParentId = t.ParentID ?? 0,
Title = t.Title,
Body = t.Body,
Children = GetChildrenByParentId(t.ID)
};
children.Add(thread);
}
return children;
}
For completeness, here's my model:
public class MCMessageCenterThread
{
public int Id { get; set; }
public int ParentId { get; set; }
public string Title { get; set; }
public string Body { get; set; }
public IEnumerable<MCMessageCenterThread> Children { get; set; }
}
I wrote something recently that does N+1 selects to load the whole tree, where N is the number of levels of your deepest path in the source object.
This is what I did, given the following self-referencing class
public class SomeEntity
{
public int Id { get; set; }
public int? ParentId { get; set; }
public string Name { get; set;
}
I wrote the following DbSet helper
using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
using System.Threading.Tasks;
namespace Microsoft.EntityFrameworkCore
{
public static class DbSetExtensions
{
public static async Task<TEntity[]> FindRecursiveAsync<TEntity, TKey>(
this DbSet<TEntity> source,
Expression<Func<TEntity, bool>> rootSelector,
Func<TEntity, TKey> getEntityKey,
Func<TEntity, TKey> getChildKeyToParent)
where TEntity: class
{
// Keeps a track of already processed, so as not to invoke
// an infinte recursion
var alreadyProcessed = new HashSet<TKey>();
TEntity[] result = await source.Where(rootSelector).ToArrayAsync();
TEntity[] currentRoots = result;
while (currentRoots.Length > 0)
{
TKey[] currentParentKeys = currentRoots.Select(getEntityKey).Except(alreadyProcessed).ToArray();
alreadyProcessed.AddRange(currentParentKeys);
Expression<Func<TEntity, bool>> childPredicate = x => currentParentKeys.Contains(getChildKeyToParent(x));
currentRoots = await source.Where(childPredicate).ToArrayAsync();
}
return result;
}
}
}
Whenever you need to load a whole tree you simply call this method, passing in three things
The selection criteria for your root objects
How to get the property for the primary key of the object (SomeEntity.Id)
How to get the child's property that refers to its parent (SomeEntity.ParentId)
For example
SomeEntity[] myEntities = await DataContext.SomeEntity.FindRecursiveAsync(
rootSelector: x => x.Id = 42,
getEntityKey: x => x.Id,
getChildKeyToParent: x => x.ParentId).ToArrayAsync();
);
Alternatively, if you can add a RootId column to the table then for each non-root entry you can set this column to the ID of the root of the tree. Then you can fetch everything with a single select
DataContext.SomeEntity.Where(x => x.Id == rootId || x.RootId == rootId)
For an example of loading in child objects, I'll give the example of a Comment object that holds a comment. Each comment has a possible child comment.
private static void LoadComments(<yourObject> q, Context yourContext)
{
if(null == q | null == yourContext)
{
return;
}
yourContext.Entry(q).Reference(x=> x.Comment).Load();
Comment curComment = q.Comment;
while(null != curComment)
{
curComment = LoadChildComment(curComment, yourContext);
}
}
private static Comment LoadChildComment(Comment c, Context yourContext)
{
if(null == c | null == yourContext)
{
return null;
}
yourContext.Entry(c).Reference(x=>x.ChildComment).Load();
return c.ChildComment;
}
Now if you were having something that has collections of itself you would need to use Collection instead of Reference and do the same sort of diving down. At least that's the approach I took in this scenario as we were dealing with Entity and SQLite.
This is an old question, but the other answers either had n+1 database hits or their models were conducive to bottom-up (trunk to leaves) approaches. In this scenario, a tag list is loaded as a tree, and a tag can have multiple parents. The approach I use only has two database hits: the first to get the tags for the selected articles, then another that eager loads a join table. Thus, this uses a top-down (leaves to trunk) approach; if your join table is large or if the result cannot really be cached for reuse, then eager loading the whole thing starts to show the tradeoffs with this approach.
To begin, I initialize two HashSets: one to hold the root nodes (the resultset), and another to keep a reference to each node that has been "hit."
var roots = new HashSet<AncestralTagDto>(); //no parents
var allTags = new HashSet<AncestralTagDto>();
Next, I grab all of the leaves that the client requested, placing them into an object that holds a collection of children (but that collection will remain empty after this step).
var startingTags = await _dataContext.ArticlesTags
.Include(p => p.Tag.Parents)
.Where(t => t.Article.CategoryId == categoryId)
.GroupBy(t => t.Tag)
.ToListAsync()
.ContinueWith(resultTask =>
resultTask.Result.Select(
grouping => new AncestralTagDto(
grouping.Key.Id,
grouping.Key.Name)));
Now, let's grab the tag self-join table, and load it all into memory:
var tagRelations = await _dataContext.TagsTags.Include(p => p.ParentTag).ToListAsync();
Now, for each tag in startingTags, add that tag to the allTags collection, then travel down the tree to get the ancestors recursively:
foreach (var tag in startingTags)
{
allTags.Add(tag);
GetParents(tag);
}
return roots;
Lastly, here's the nested recursive method that builds the tree:
void GetParents(AncestralTagDto tag)
{
var parents = tagRelations.Where(c => c.ChildTagId == tag.Id).Select(p => p.ParentTag);
if (parents.Any()) //then it's not a root tag; keep climbing down
{
foreach (var parent in parents)
{
//have we already seen this parent tag before? If not, instantiate the dto.
var parentDto = allTags.SingleOrDefault(i => i.Id == parent.Id);
if (parentDto is null)
{
parentDto = new AncestralTagDto(parent.Id, parent.Name);
allTags.Add(parentDto);
}
parentDto.Children.Add(tag);
GetParents(parentDto);
}
}
else //the tag is a root tag, and should be in the root collection. If it's not in there, add it.
{
//this block could be simplified to just roots.Add(tag), but it's left this way for other logic.
var existingRoot = roots.SingleOrDefault(i => i.Equals(tag));
if (existingRoot is null)
roots.Add(tag);
}
}
Under the covers, I am relying on the properties of a HashSet to prevent duplicates. To that end, it's important that the intermediate object that you use (I used AncestralTagDto here, and its Children collection is also a HashSet), override the Equals and GetHashCode methods as appropriate for your use-case.