I don't have much code to post, and I'm quite confused on where to start. There's a lot of documentation online and I can't seem to find what I'm looking for.
Suppose I have this query result saved into a StatementResult variable:
result = session.run("MATCH (n:person {tag1: 'Person1'})"
+ "RETURN [(n)-->(b) WHERE b:type1 | m.tag2]")
In the Neo4j browser, this returns a list of exactly what I'm looking for. My question is how we can access this in Java. I know how to access single values, but not a list of this type.
Any help would be appreciated.
Thanks.
Usually you just iterate over the statement results, to access each record and then with each record you can access each named column. You didn't use any names.
The column will return Value objects which you then can turn into the types you expect, so in your case into a list with asList().
See the API docs for StatementResult and Value.asList()
also your statement is not correct you probably meant b where you wrote m and you need to name your column to access it
Related
I want to filter results by a specific value in the aggregated array in the query.
Here is a little description of the problem.
Section belongs to the garden. Garden belongs to District and District belongs to the province.
Users have multiple sections. Those sections belong to their gardens and they are to their Districts and them to Province.
I want to get user ids that have value 2 in district array.
I tried to use any operator but it doesn't work properly. (syntax error)
Any help would be appreciated.
ps: This is possible writing using plain SQL
rs = dslContext.select(
field("user_id"),
field("gardens_array"),
field("province_array"),
field("district_array"))
.from(table(select(
arrayAggDistinct(field("garden")).as("gardens_array"),
arrayAggDistinct(field("province")).as("province_array"),
arrayAggDistinct(field("distict")).as("district_array"))
.from(table("lst.user"))
.leftJoin(table(select(
field("section.user_id").as("user_id"),
field("garden.garden").as("garden"),
field("garden.province").as("province"),
field("garden.distict").as("distict"))
.from(table("lst.section"))
.leftJoin("lst.garden")
.on(field("section.garden").eq(field("garden.garden")))
.leftJoin("lst.district")
.on(field("district.district").eq(field("garden.district")))).as("lo"))
.on(field("user.user_id").eq(field("lo.user_id")))
.groupBy(field("user.user_id"))).as("joined_table"))
.where(val(2).equal(DSL.any("district_array"))
.fetch()
.intoResultSet();
Your code is calling DSL.any(T...), which corresponds to the expression any(?) in PostgreSQL, where the bind value is a String[] in your case. But you don't want "district_array" to be a bind value, you want it to be a column reference. So, either, you assign your arrayAggDistinct() expression to a local variable and reuse that, or you re-use your field("district_array") expression or replicate it:
val(2).equal(DSL.any(field("district_array", Integer[].class)))
Notice that it's usually a good idea to be explicit about data types (e.g. Integer[].class) when working with the plain SQL templating API, or even better, use the code generator.
I am using JDBI to iterate through a resultset via streams. Currently mapToMap is causing problems when there is a column with the same name in the result. What I need is just the values without the column names.
Is there a way to map the results to an Object list/array? The docs does not have an example for this. I would like to have something like
query.mapTo(List<Object>.class).useStream(s -> { . . .})
First of all - what kind of use case would allow you not care at all about the column name but only the values? I am genuinely curious
If it does make sense, it is trivial to implement a RowMapper<List<Object>> in your case, which runs through all the columns by index and puts the results of rs.getObject(i) into a list.
Question:
What might the following code be expected to do?
var notifications = Notification.Query
.Where(n=>n.UserVersion==Oracle.CurrentUserID)
.Where(n=>n.IsUnread==true)
.OrderByDescending
My Answer:
Outputs a query result that is stored as variable ‘notifications’ where rows under ‘UserVersion’ field matches with ‘CurrentlUserId’ in Oracle and the ‘IsUnread’ is true. It’s set to order by latest date and onwards and it will display the first 25 rows.
Is this correct? Also what type of programming language is this regarding as I have not across this before.
Thank you in advance.
This looks like C# code. The result isn't really a query result, but rather an IEnumerable that contains items from the Notification.Query collection that match the criteria specified.
https://msdn.microsoft.com/en-us/library/vstudio/bb534803(v=vs.100).aspx
https://msdn.microsoft.com/en-us/library/vstudio/Bb534855(v=VS.100).aspx
I am new to mongodb and I am trying to sort all my rows by date. I have records from mixed sources and I trying to sort it separately. I didn't update the dateCreated while writing into db for some records. Later I found and I added dateCreated to all my records in the db. Say I have total of 4000 records, first 1000 I don't have dateCreated. Latest 3000 has that column. Here I am trying to get the last Updated record using dateCreated column. Here is my code.
db.person.find({"source":"Naukri"}&{dateCreated:{$exists:true}}).sort({dateCreated: 1}).limit(10)
This code retruns me some results (from that 1000 records) where I can't see that dateCreated column at all. Moreover if I change (-1) here {dateCreated: -1} I am getting results from some other source, but not Naukri.
So I need help this cases,
How do I sort by dateCreated to get the latest updated record and by sources also.
I am using Java API to get the records from Mongo. I'd be grateful if someone helps me to find how I will use the same query with java also.
Hope my question is clear. Thanks in advance.
From the documentation you will (and you will, won't you - nod yes) read, you will find that the first argument to the find command you are using is what is called a query document. In this document you are specifying a list of fields and conditions, "comma" separated, which is the equivalent of an and condition in declarative syntax such as SQL.
The problem with your query is it was not valid, and did not match anything. The correct syntax would be as follows:
db.person.find({"source":"Naukri", dateCreated:{$exists:true}})
.sort({dateCreated: -1})
.limit(10)
So now this will filter by the value provided for "source" and where the "dateCreated" field exists, meaning it is there and it contains something.
I recommend looking at the links below, the first of the two concerned with structuring mongoDB queries and the find method and it's arguments. All of the functionality translates to every language implementation.
As for the Java API and how to use, there are different methods depending on which you are comfortable with. The API provides a BasicDBObject class which is more or less equivalent to the JSON document notation, and is sort of a hashmap concept. For something a bit more along the lines of the shell methods and a helper to be a little more like some of the dynamic languages approach, there is the QueryBuilder class which the last two links give example and information on. These allow chaining to make your query more readable.
There are many examples on Stack Overflow alone. I suggest you take a look.
http://docs.mongodb.org/manual/tutorial/query-documents/
http://docs.mongodb.org/manual/reference/method/db.collection.find/
How to do this MongoDB query using java?
http://api.mongodb.org/java/2.2/com/mongodb/QueryBuilder.html
Your query is not correct.Update it as follows :
db.person.find({"source":"Naukri", dateCreated:{$exists:true}}).sort({dateCreated: 1}).limit(10)
In Java, you can do it as follows :
Mongo mongo = ...
DB db = mongo.getDB("yourDbName");
DBCollection coll = db.getCollection("person");
DBObject query = new BasicDBObject();
query.put("source", "Naukri");
query.put("dateCreated", new BasicDBObject($exists : true));
DBCursor cur = coll.find(query).sort(new BasicDBObject("dateCreated", 1)).limit(10);
while(cur.hasNext()) {
DBObject obj = cur.next();
// Get data from the result object here
}
I am going through a final refinement posted by the client, which needs me to do a case-insensitive query. I will basically walk through how this simple program works.
First of all, in my Java class, I did a fairly simple webpage parsing:
title=(String)results.get("title");
doc = docBuilder.parse("http://" + server + ":" + port + "/exist/rest/db/wb/xql/media_lookup.xql?" + "&title=" + title);
This Java statement references an XQuery file "media_lookup.xql" which is stored on localhost, and the only parameter we are passing is the string "title".
Secondly, let's take at look at that XQuery file:
$title := request:get-parameter('title',""),
$mediaNodes := doc('/db/wb/portfolio/media_data.xml'),
$query := $mediaNodes//media[contains(title,$title)],
Then it will evaluate that query. This XQuery will get the "title" parameter that are passes from our Java class, and query the "media_data" xml file stored in the database, which contains a bunch of media nodes with a 'title' element node. As you may expect, this simple query will just match those media nodes whose 'title' element contains a substring of what the value of string 'title' is. So if our 'title' is "Chi", it will return media nodes whose title may be "Chicago" or "Chicken".
The refinement request posted by the client is that there should be NO case-sensitivity. The very intuitive way is to modify the XQuery statement by using a lower-case function in it, like:
$query := $mediaNodes//media[contains(lower-case(title/text(),lower-case($title))],
However, the question comes: this modified query will run my machine into memory overflow. Since my "media_data.xml" is quite huge and contains thouands of millions of media nodes,
I assume the lower-case() function will run on each of the entries, thus causing the machine to crash.
I've talked with some experienced XQuery programmer, and they think I should use an index to solve this problem, and I will definitely research into that. But before that, I am just posting this problem here to get other ideas or any suggestions, do you think any other way may help? for example, could I tweak the Java parse statement to realize the case-insensitivity? Since I think I saw some people did some string concatenation by using "contains." in Java before passing it to the server.
Any idea or help is welcomed.
The refinement request posted by the
client is that there should be NO
case-sensitivity. The very intuitive
way is to modify the XQuery statement
by using a lower-case function in it,
like:
$query := $mediaNodes//media
[contains(lower-case(title/text(),lower-case($title))],
However, the question comes: this
modified query will run my machine
into memory overflow. Since my
"media_data.xml" is quite huge and
contains thousands of millions of media
nodes, I assume the lower-case()
function will run on each of the
entries, thus causing the machine to
crash.
Such fears are not justified.
Any sane implementation of XPath uses automatic memory for its functions. This means that the memory required for evaluating a particular predicate, including the result of lower-case() becomes freed (in languages with no garbage collection) or unreferenced and ready for garbage collection immediately after the evaluation of the predicate.
A table index probably is not the solution as absebse of an index will slow things down, but not trigger a memory overflow.
I think your best bet is to duplicate the title in your database copying it into an all-lowercase (or uppercase with makes more clear that it was converted) and query the alternate title while presenting the normal title.
To save some processing to you can do the case coversion of $product before the query.
You can drop the ampersand in your URL, I'm not sure all webservers parse the ?& correctly.