I know this may sound nonsense but I will try my best to explain the problem that I am facing with neo4jClient.
I developing a Social TaskManagment Software. and for the server side code and data Storage I choose to have neo4j (neo4jClient) and C# in place.
in Our software Imagine a User : (mhs) Post a Task of "#somebody please help me on #Neo4j #cypher" the task would be decorated with some fancy character including (# # + /) the obove post will be save in neo4j as graph like this :
(post:Post {Text : #somebody please help me on #Neo4j})-[Has_HashTag]-(neo4j:HashTag)
(post:Post)-[Has_HashTag]-(Cypher: HashTag)
(post:Post)-[Has_Author)-[mhs:User]
(post:Post)-[Has_MentionedUser)-[Somebody:User]
Now Imagine User #mhs is trying to search the Post that Have HashTag of #Neo4j and mentioned to #somebody
Here I am building (hand Craft) a Cypher Query Including the 2 seach Paramerts in Cypher with Some Fancy C# code which result the blow Cypher Query:
MATCH (nodes)-[r]-(post:Post),
(post:Post)-[:HAS_MentionedUsers]->(assignee1307989068:User),
(nodes)-[r]-(post:Post)-[:HAS_HashTags]->(Hashtag1482870844:HashTag)
WHERE (assignee1307989068.UserName = "somebody") AND (Hashtag1482870844.Value = "neo4j")
RETURN post AS Post, Collect(nodes) as nodes
ORDER BY post.creationDate
the above cypher will return a post with just all the nodes of the post that is not included in Where clause.
my question is how to include all the Nodes related to the Targeted (post) without including them in Return part of the cypher. Something like return (*).
The Other problem is How can I deserialize the result set into C# without knowing what shape it may have.
The Search method that I am producing the mentioned Cypher is as fallow:
public List<PostNode> Search(string searchterm)
{
List<string> where = new List<string>();
var tokenizedstring = searchterm.Split(' ');
var querystring = new StringBuilder();
var relatedNodes = new List<string>();
var q = new CypherFluentQuery(_graphClient) as ICypherFluentQuery;
foreach (var t in tokenizedstring)
{
_commandService.BuildPostQueystring(t, ref querystring, ref where, ref relatedNodes);
}
if (querystring[querystring.Length - 1] == ',')
querystring = querystring.Remove(querystring.Length - 1, 1);
q = q.Match(querystring.ToString());
int i = 1;
if (where.Count > 0)
q = q.Where(where[0]);
while (i < where.Count)
{
q = q.AndWhere(where[i]);
i++;
}
var rq = q.Return(
(post, nodes) => new PostNode
{
Post = post.As<Node<string>>(),
Nodes = nodes.CollectAs<string>()
})
.OrderBy("post.creationDate");
var results = rq.Results.ToList();
//foreach (var result in results)
//{
// //dynamic p = JsonConvert.DeserializeObject<dynamic>(result.Post.Data);
// //dynamic d = JsonConvert.DeserializeObject<dynamic>(result.Nodes.Data);
//}
return results;
}
}
//Some Helper Class just to cast the result.
public class PostNode
{
public Node<string> Post { get; set; }
public IEnumerable<Node<string>> Nodes { get; set; }
}
But as you may noticed it does not have the nodes that is included in the search term via Where Clause in Cypher Query.
I am really stopped here for a while, as I can not provide any decent solution for this. so your help may save me a lot.
may be i am totally in a wrong direction so please help in any way you can think of.
It appears that a list of UNKNOWN related nodes are being provisioned, so one of this:
Scenario A
It doesn't matter what EXACTLY those related nodes are, I just want them.
Question: What is intention of retrieving those unknown but related nodes? By answering this chances are this query could be improved for good.
Scenario B
These unknown related nodes are actually known! It's just they are not fully known at time of query execution however down the road somewhere in C# code we will have things like this
if (nodes.Any(_ => _ is HashTag) {...}
Question:
This type of behaviour requires to KNOW the type. Even with reflection or C# dynamic stuff that requirement is still there because Neo4jClient has no way of correlating a bag of JSON data coming from Neo4j into any local type. When Neo4jClient receives bulk of data over wire somehow it should know what type would YOU prefer to represent. This is why queries are always like this:
Return((a, p) => new
{
Author = a.As<Author>(), //we expect node content to be represented as Author
Post = p.As<Post>()
})
Neo4jClient does NOT preserve C# types inside your Neo4j database. It would have been nasty to do so. However, idea behind it is that you shouldn't find yourself desperate for it and if you do so then I would recommend looking for problem somewhere else i.e. why would you rely on your client library to describe your domain for you?
Related
I am currently trying to unwind a list of objects that I want to merge to the database using the Neo4J Client. What I would like to do is unwind the list and create the nodes with a label generated based on a property from the items themselves instead of hardcoding a label name. From what I can find I have to use the APOC merge method to do so. However, I am unable to translate this to the Neo4J client. In the neo4J explanation they yield a node after the apoc.merge.node call and then return the node. However, I cannot simply return the node nor can I set the node (I got to the point of just messing about, and at one point I got the labels to work but it overwrote all properties with the last item in the list).
I seem to miss something fundamental but i'm not quite sure what. Does anyone here know how to do this with neo4J client (and if possible, give a bit of an explanation what is going on)? I am very new to the development world and I feel I am just missing a crucial piece of understanding when it comes to this..
The code that I tried that turned all properties into the last node's properties but at least created the labels as I expected:
public async void CreateBatchItems(List<TToDataBase> itemList)
{
await Client.Cypher
.Unwind(itemList, "row")
.Merge("(n)")
.With("row, n")
.Call("apoc.merge.node([n.Name], n)").Yield("node")
.Set("n += node")
.ExecuteWithoutResultsAsync();
}
Thank you in advance!
Edit:
Some clarification about the input:
The objects are actually very basic, as (at least for now), they merely contain a name and an objectID (and these object ID's are later used to create relations). So its a very basic class with two properties:
public class Neo4JBaseClass
{
public Neo4JBaseClass() { }
public Neo4JBaseClass(string name, string objectId)
{
Name = name;
ObjectId = objectId;
}
[JsonProperty(PropertyName = "ObjectId")]
public string ObjectId { get; set; }
[JsonProperty(PropertyName = "Name")]
public string Name { get; set; }
}
I have also tried a slight variation where this class also has the added property
[JsonProperty(PropertyName = "PropertyMap")]
public IProperty PropertyMap { get; set; }
where PropertyMap is another basic object holding the name and objectId. This seemed like a good idea for future proofing anyway, so the propertylist can be easily expanded without having to change the base object.
[EDITED]
The main issue is that Merge("(n)") matches any arbitrary node that already exists.
You have not shown the data structure for each element of itemList, so this answer will assume it looks like this:
{Name: 'SomeLabel', id: 123, Props: {foo: 'xyz', bar: true}}
With above data structure, this should work:
public async void CreateBatchItems(List<TToDataBase> itemList)
{
await Client.Cypher
.Unwind(itemList, "row")
.Call("apoc.merge.node([row.ObjectId], row.id)").Yield("node")
.Set("node += row.Props")
.ExecuteWithoutResultsAsync();
}
[UPDATE]
The data structure you added to your question is very different than what I had imagined. Since neither of the properties in a row is a map, .Set("node += row.Props") would generate an error.
Using your data structure for each row, this might work:
public async void CreateBatchItems(List<TToDataBase> itemList)
{
await Client.Cypher
.Unwind(itemList, "row")
.Merge("(n:Foo {id: row.ObjectId})")
.Set("n += row.Name")
.ExecuteWithoutResultsAsync();
}
This code assigns the node label Foo to all the generated nodes. A node should always have a label, which improves clarity and also tends to improve efficiency -- especially if you also create indexes. For example, an index on :Foo(id) would make the above query more efficient.
This code also assumes that the id property is supposed to contain a unique Foo node identifier.
In my system, I would like to intercept and change Cypher queries as they come in, one alternative is to modify them before sending them from my middle layer to the graph - but is there a way to have a plugin do the conversion for me in the graph itself?
I'd like to do some of the following:
If someone identifying themselves as members of group A, imagine I'd like to change their request from:
MATCH(f:Film)-[r:REVIEWED_BY]-(u:User {id:"1337"})
to:
MATCH(p:Product)-[p:PURCHASED_BY]-(u:User {id:"1337"})
Is something like this possible? Or do I have to write the traversals in Java directly to achieve this?
Of course you can. You can do ANYTHING in Neo4j. Just grab the cypher string in an unmanaged extension that receives a post request, alter it any way you want, execute it with the graphdb.execute method and return the result as normal.
#POST
#Path("/batch")
public Response alterCypher(String body, #Context GraphDatabaseService db) throws IOException, InterruptedException {
ArrayList<Result> results = new ArrayList<>();
// Validate our input or exit right away
HashMap input = Validators.getValidCypherStatements(body);
ArrayList<HashMap> statements = (ArrayList<HashMap>)input.get("statements");
for (HashMap statement : statements) {
// write the alterQuery method to change the queries.
String alteredQuery = alterQuery((String)statement.get("statement"));
Result result = db.execute(alteredQuery, (Map)statement.getOrDefault("parameters", new HashMap<>()));
results.add(result);
}
// or go the results and return them however you want
// see https://github.com/dmontag/neo4j-unmanaged-extension-template/blob/master/src/main/java/org/neo4j/example/unmanagedextension/MyService.java#L36
return Response.ok().build();
}
At this time it's not possible to extend or modify Cypher queries.
If you need that I recommend you to use Transaction Event API - http://graphaware.com/neo4j/transactions/2014/07/11/neo4j-transaction-event-api.html
With that you should be able to change what query returns.
I am building an ASP.NET MVC application using the Repository pattern. A typical method in my Repository is as follows
public IList<T> Select<T>(string cacheKey, string Sql, object filter) where T: new()
{
IList<T> items = MemoryCache.Default.Get(cacheKey) as IList<T>;
if (items == null || !items.Any())
{
items = Connection.Select<T>(Sql, filter);
MemoryCache.Default.Add(cacheKey, items, DateTime.Now.AddMinutes(120));
}
return items;
}
and it is being used as follows
IEnumerable<OSADCOL> osadcols = Repository.Select<OSADCOL>("OSADCOLS__TblId=" + Id, "TBLid = #id", new { id = Id });
In the above mentioned example OSADCOL is a model in my app and represents a Table with the same name in my Database. The Connection.Select function is ORMlite function. I don't use Entity Framework for performance issues. My problem is the following. I am currently cashing the result set for future relevance but I am doing it in a hard coded way. I am caching the result set for 2 hours. It is obvious that a proper implementation would be to discard my cashed data when the OSADCOL's table data changes. It seems that I have to use SQLDependency or SQLCacheDependency. The questions are the following:
How am I going to use SQLDependency or SQLCacheDependency with this Repository?
What is the actual difference between these 2?
It is mentioned in some forums that SQLDependency creates memory leaks? Is that true? And If yes is there an alternative approach?
Any Ideas?
I am using RavenDB 2.0 unstable.
Is it possible to query RavenDB 2.0 with a lambda or similar technique (linq?) from F#?
Here is intent example code. I am attempting to get all the posts in last 72 hours. Its wrong, but it gets the idea across.
static member public GetTopPosts _ =
use store = (new DocumentStore(Url = Docs.serverUrl, DefaultDatabase = Docs.dbName )).Initialize()
use session = store.OpenSession()
let result = session.Query<Post>().Where(fun x -> x.Date > DateTime.Now - new TimeSpan(72,0,0))
...
How can something like this be accomplished?
Yes you can do this.
You can find an example of this in FAKE
In your case your query would look something like this
let getTopPostsAsOf date =
use session = docStore.OpenSession()
query {
for post in session.Query<Post>() do
where (post.Date > date)
select post
} |> Seq.toArray
this would then be called with
let result = getTopPostsAsOf (DateTime.Now - TimeSpan.FromHours(72))
A couple of things to note.
The DocumentStore should be created once and only once at the startup of the application.
Also typically only a small set of library calls can be used within the query expressions, hence why I pass in the already computed date. The reason for this is because these expression trees end up getting serialized and executed within raven db engine.
With a plain connection to SQL Server, you can specify what columns to return in a simple SELECT statement.
With EF:
Dim who = context.Doctors.Find(3) ' Primary key is an integer
The above returns all data that entity has... BUT... I would only like to do what you can with SQL and get only what I need.
Doing this:
Dim who= (From d In contect.Doctors
Where d.Regeneration = 3
Select New Doctor With {.Actor = d.Actor}).Single
Gives me this error:
The entity or complex type XXXXX cannot be constructed in a LINQ to Entities query.
So... How do I return only selected data from only one entity?
Basically, I'm not sure why, but Linq can't create the complex type. It would work if you were creating a anonymous type like (sorry c# code)
var who = (from x in contect.Doctors
where x.Regeneration == 3
select new { Actor = x.Actor }).Single();
you can then go
var doctor = new Doctor() {
Actor = who.Actor
};
but it can't build it as a strongly typed or complex type like you're trying to do with
var who = (from x in contect.Doctors
where x.Regeneration == 3
select new Doctor { Actor = x.Actor }).Single();
also you may want to be careful with the use of single, if there is no doctor with the regeneration number or there are more than one it will throw a exception, singleordefault is safer but it will throw a exception if there is more than one match. First or Firstordefault are much better options First will throw a exception only if none exist and Firstordefault can handle pretty much anything
The best way to do this is by setting the wanted properties in ViewModel "or DTO if you're dealing with upper levels"
Then as your example the ViewModel will be:
public class DoctorViewModel{
public string Actor {get;set;}
// You can add as many properties as you want
}
then the query will be:
var who = (From d In contect.Doctors
Where d.Regeneration = 3
Select New DoctorViewModel {Actor = d.Actor}).Single();
Sorry i wrote the code with C# but i think the idea is clear :)
You can just simply do this:
Dim who= (From d In contect.Doctors
Where d.Regeneration = 3
Select d.Actor).Single
Try this
Dim who = contect.Doctors.SingleOrDefault(Function(d) d.Regeneration = 3).Actor