So, I need to write something in Rails 3 that does a query to a MongoDB (If you don't know mongo I don't need the code just some ideas) that can query the data for close matches. For instance, let us say you are searching a collection for {item : a, item2 : b, item3 : c}. And exact match would have all three, but I also want matches that omit one of the three keys. I have two theories on how I should handle this. One would be to do multiple queries to omit certain parts of the data and the other would be to write a complex or statement. I don't feel these are the best solutions though. Could anyone else suggest something to me? Even if it is from an SQL perspective, that would work for me.
I do need something that can be done fast. This is for a search that needs to return results as fast as possible.
Yet another approach would be to use MapReduce.
With it you can calculate how many fields a document matches.
Though it's not very performant approach at the moment (but one of the most flexible).
The code can be something like this:
var m = function() {
var fieldsToMatch = {item: a, item2: b, item3: c};
for(var k in fieldsToMatch) {
if(this[k] == fieldsToMatch[k]) {
emit(this.id, {count : 1}); // emit 1 for each field matched
}
}
};
var r = function(k, vals) {
var result = {count: 0};
vals.forEach(function(v) {
result.count += v.count;
});
return result;
}
db.items.mapReduce(m, r, {out: 'out_collection'});
Why dont you just use mongodb OR, in ruby (using mongoid) you can do this by
Collection.any_of({:item => a, :item2 => b, item3 => c},{:item => a, :item2 => b},{:item => a, :item3 => c},{:item2 => b, item3 => c})
which is equivalent to
db.Collection.find({$or:[{item:a,item2:b,item3:c}],[{item:a,item2:b}],[{item:a,item3:c}],[{item2:b,item3:c}]})
Related
I have a function called updateAnswer with multiple dynamic parameters.
updateAnswer(key, answer, array = false) {
if (array) {
if(this.answers.contains.find(element => element === answer)) {
//Delete item from array if already element already exists in this.answers.contains array.
} else {
Vue.set(this.answers, key, [...this.answers.contains, answer]);
}
} else {
Vue.set(this.answers, key, answer);
}
},
I'd like to know how delete an item in the array if the value already exists in the array.
You can use method called splice:
Just reference on your array and set values in the brackets the first is referenced on the position, the second is how many datas you want to splice/delete.
The function looks like this:
this.array.splice(value, value)
Lets see on an example - you have array food= [apple, banana, strawberry] than I'm using this.food.splice(1,1)..
my array looks now like this food = [apple, strawberry] - first value in my brackets are the position, the second one is the amount of "numbers" you want to delete.
Hopefully this helps you out!
I suppose each value in this.answers.contains is unique?
Anyways, if you just want to delete the item if already exists, I suggest filter(). It should look like below:
if(this.answers.contains.find(element => element === answer)) {
this.answers.contains = this.answers.contains.filter(c => c !== answer)
}
Also, the if condition if(this.answers.contains.find(element => element === answer)) could also be replaced by if(this.answers.contains.includes(answer))
Hope that could help you.
How can i dynamically change the selected columns in the generated sql query when using a linq expression?
Its a new session for each time the query is executed.
Even when I set the MapExp as null after first creation an then changing the bool value to false, it still generates the column in the sql query.
The code runs in a wpf application.
System.Linq.Expressions.Expression<Func<Entity, Model>> MapExp = x => new Model
{
Id=xId,
Count= LoadFormulaField ? x.Count: null,
...
};
var result = session.Query<Entity>().Select(MapExp))
Your problem seems to be the ternary-conditional as part of the expression which is causing the "Count" column to always be queried.
One option to avoid this could be:
var query = session.Query<Entity>();
IQueryable<Model> result = null;
if (LoadFormulaField)
{
result = query.Select(x => new Model
{
Id = x.Id,
Count = x.Count,
});
}
else
{
result = query.Select(x => new Model
{
Id = x.Id,
});
}
Which would get a little less ugly if you separate in a couple of methods I think.
I was trying to convert a query from SQL into Scala code with Slick, but I have got a compiler error in filter clause: constructor cannot be instantiated to expected type.
My code in Slick:
val subquery = (for {
pit <- PassInTripTable.table
t <- TripTable.table if pit.tripNoFk === t.tripNo
} yield (pit, t))
.map{ case (pit, t) => ( pit, Case.If(t.townFrom <= t.townTo).Then(t.townFrom ++ t.townTo).Else(t.townFrom ++ t.townTo) )}
.groupBy(_._1.idPsgFk)
.filter{ case ((pit, count), group) => ( group.map(_._2).countDistinct === 1)}
.map(_._1)
val query = PassengerTable.table.filter(_.idPsg in subquery).map(_.name)
db.run(query.result)
The query in SQL itself:
select name from passenger
where id_psg in
(
select id_psg from trip t,pass_in_trip pit
where t.trip_no=pit.trip_no
group by id_psg
having count(distinct case when town_from<=town_to then town_from+town_to else town_to+town_from end)=1
)
I would be very grateful if someone helped me to find an error.
From looking at your code, it looks like the type you are matching on is not supposed to be "((pit, count), group)".
groupBy in Slick only returns a collection of Tuple2s.
http://slick.lightbend.com/doc/3.0.0/queries.html
So, the filter might look something like...
.filter{ case (pit, count) => ( count.map(_._2).countDistinct === 1)}
The problem is that Slick .groupBy requires a .map call with aggregating functions afterwards. You can find detailed information here.
So, try this:
.groupBy(_._1.idPsgFk)
.map{ case (key, group) => (key, group.map(_._2).countDistinct)}
.filter{ case (_, count) => count === 1}
.map(_._1)
P.S.
I've also found "bad smells" in your code. You get pairs as a result of for-comrehension, but it looks like standard join would be more appropriate here (and more efficient), something like:
PassInTripTable.table.join(TripTable.table).on(_.tripNoFk === _.tripNo)
.map{ case (pit, t) => ...}
And why would you use such condition:
Case.If(t.townFrom <= t.townTo).Then(t.townFrom ++ t.townTo).Else(t.townFrom ++ t.townTo)? Its branches are the same, so equals to t.townFrom ++ t.townTo.
I have array of objects, objects have properties say "a", "b" and "c".
Now I need to filter out objects which has unique values of "a & b".
However c plays role on which objects to keep and which ones to reject.
If I do uniqBy on properties a and b, I will be blindly rejecting other objects. It will keep the first object it encounters in the array and reject all other duplicates.
Let me know if you need more clarification on the question.
This is how I found the uniq objects based on two properties.
var uniqArray= _.uniqBy(obj, function(elem) { return [elem.a, elem.b].join(); })
lodash uniq - choose which duplicate object to keep in array of objects
Do we have better solution?
Here is an example of input and expected output
Input: var arrayOfObj = [{a:1, b:1, c:2}, {a:1,b:1,c:1}, {a:2, b:2,c:2}];
Output: arrayOfObj = [{a:1,b:1,c:1}, {a:2, b:2,c:2}]; there should not be any duplicate a1,b1 combination
According to Lodash documentation, the order of result values is determined by the order they occur in the array. Therefore you need to order the array using the 'c' property in order to get the expected result.
To do so, you can use _.sortBy. It orders a collection in asc order based on a property or an iteratee. I think your problem could be solved using a property directly though you could use a function to provide a more accurate comparator if needed.
After that, you just perform the uniqBy action and retrieve the result:
var res = _(arrayOfObj)
.orderBy('c')
.uniqBy('a', 'b')
.value();
console.log(res);
Here's the fiddle.
As I read in the comments, your 'c' property is a timestamp. If you want to order from latest to newest, you can pass an iteratee to sort by in order to reverse the natural order by 'c':
var res = _(arrayOfObj)
.orderBy(function(obj) {
return -(+obj.c);
})
.uniqBy('a', 'b')
.value();
console.log(res);
You can check it out in this update of the previous fiddle. Hope it helps.
Would help to know what the actual data is and what you want to achieve with it. Here's an idea: group your objects based on a and b, then from each grouping, select one item based on c.
var arrayOfObj = [
{a:1, b:1, c:2},
{a:1, b:1, c:1},
{a:2, b:2, c:2}
];
var result = _.chain(arrayOfObj)
.groupBy(function (obj) {
return obj.a.toString() + obj.b.toString();
})
.map(function (objects) {
//replace with code to select the right item based on c
return _.head(objects);
}).value();
Really stuck with Linq to SQL grouping and summing, have searched everywhere but I don't understand enough to apply other solutions to my own.
I have a view in my database called view_ProjectTimeSummary, this has the following fields:
string_UserDescription
string_ProjectDescription
datetime_Date
double_Hours
I have a method which accepts a to and from date parameter and first creates this List<>:
List<view_UserTimeSummary> view_UserTimeSummaryToReturn =
(from linqtable_UserTimeSummaryView
in datacontext_UserTimeSummary.GetTable<view_UserTimeSummary>()
where linqtable_UserTimeSummaryView.datetime_Week <= datetime_To
&& linqtable_UserTimeSummaryView.datetime_Week >= datetime_From
select linqtable_UserTimeSummaryView).ToList<view_UserTimeSummary>();
Before returning the List (to be used as a datasource for a datagridview) I filter the string_UserDescription field using a parameter of the same name:
if (string_UserDescription != "")
{
view_UserTimeSummaryToReturn =
(from c in view_UserTimeSummaryToReturn
where c.string_UserDescription == string_UserDescription
select c).ToList<view_UserTimeSummary>();
}
return view_UserTimeSummaryToReturn;
How do I manipulate the resulting List<> to show the sum of the field double_Hours for that user and project between the to and from date parameters (and not separate entries for each date)?
e.g. a List<> with the following fields:
string_UserDescription
string_ProjectDescription
double_SumOfHoursBetweenToAndFromDate
Am I right that this would mean I would have to return a different type of List<> (since it has less fields than the view_UserTimeSummary)?
I have read that to get the sum it's something like 'group / by / into b' but don't understand how this syntax works from looking at other solutions... Can someone please help me?
Thanks
Steve
Start out by defining a class to hold the result:
public class GroupedRow
{
public string UserDescription {get;set;}
public string ProjectDescription {get;set;}
public double SumOfHoursBetweenToAndFromDate {get;set;}
}
Since you've already applied filtering, the only thing left to do is group.
List<GroupedRow> result =
(
from row in source
group row by new { row.UserDescription, row.ProjectDescription } into g
select new GroupedRow()
{
UserDescription = g.Key.UserDescription,
ProjectDescription = g.Key.ProjectDescription,
SumOfHoursBetweenToAndFromDate = g.Sum(x => x.Hours)
}
).ToList();
(or the other syntax)
List<GroupedRow> result = source
.GroupBy(row => new {row.UserDescription, row.ProjectDescription })
.Select(g => new GroupedRow()
{
UserDescription = g.Key.UserDescription,
ProjectDescription = g.Key.ProjectDescription,
SumOfHoursBetweenToAndFromDate = g.Sum(x => x.Hours)
})
.ToList();