Hi I am trying to query my database by a specific property. Multiple entries in my database may have the same value for the property but I want it to return only the first entry that has that distinct value for the property.
For example, if my domain has a code property, then there might be an entry where "code" = "boy", and there might be another one where "code" = "girl" and there might be yet another one where again "code" = "boy". I want to query it so I get the first entry where "code" = "boy" and the entry where "code" = girl" but not the third entry where code is again equal to boy.
I was able to get the distinct code values from the database using both createCriteria() or namedQueries() but I am not able to get the whole object, just the value of code. How can I get the actual object?
Thinking about I came with an HQL query:
select d
from Domain d
where d.id = (select min(d1.id)
from Domain d1
where d1.code = d.code)
Related
I am new to Neo4j and graph databases. I am trying to create a simple graph DB, but my MATCH query is returning null values. How do I avoid nulls or any errors in my coding?
Create DB
CREATE
(d2:CorNode:course:dscor{Cors_Name:'DataScience_Sem2',Start_Date:'January2018',No_Students:[tointeger(10)]})-[:sem2dsrelation{Name:'Semester2',Cor_Name:'Data Science',A_Y:'AY2017-18',Cor_Node:'CMM534'}]->(Rob:FLNode:course:dscor{Name_F:'Rob Lothian', Role:'Leader',Mod_code:'CMM534'}),
(d2)-[:sem2dsrelation{Name:'Semester2', Cor_Name:'Data Science',A_Y:'AY2017-18',Cor_Node:'CMM534'}]->(Eyad:FLNode:course:dscor{Name_F:'Eyad Elyan',Role:'Leader',Mod_code:'CMM534'}),
(d2)-[:sem2dsrelation{Name:'Semester2', Cor_Name:'Data Science',A_Y:'AY2017-18',Cor_Node:'CMM507'}]->(David:FLNode:course:dscor{Name_F:'David Lonie', Role:'Leader', Mod_code:'CMM507'}),
(d2)-[:sem2dsrelation{Name:'Semester2',Cor_Name:'Data Science', A_Y:'AY2017-18',Cor_Node:'CMM535'}]->(Rob),
(d1:CorNode:course:dscor{Cors_Name:'DataScience_Sem1',Start_Date:'Septemer2017',No_Students:[tointeger(25)]})-[:sem1dsrelation{Name:'Semester1',Cor_Name:'Data Science',A_Y:'AY2017-18',Cor_Node:'CMM524'}]->(Rob),
(d1)-[:sem1dsrelation{Name:'Semester1', Cor_Name:'Data Science',A_Y:'AY2017-18',Cor_Node:'CMM531'}]->(Eyad),
(d1)-[:sem1dsrelation{Name:'Semester1', Cor_Name:'Data Science',A_Y:'AY2017-18',Cor_Node:'CMM510'}]->(Ines:FLNode:course:dscor{Name_F:'Ines Arana',Role:'Leader',Mod_code:'CMM510'})
Query DB
MATCH (:dscor)-[ds1:sem1dsrelation{Name:'Semester1',Cor_Name:'Data Science'}]-(FLNode:dscor)
RETURN DISTINCT [FLNode.Name_F,ds1.Cor_Node]
You basically have a typo. In (FLNode:dscor), "FLNode" is being used a a variable name instead of as a label.
To fix this, you need to assign a variable name (say, x) to the node, make sure FLNode is specified to be a label (by putting a : in front of it), and then use x in the result. Like so:
MATCH (:dscor)-[ds1:sem1dsrelation{Name:'Semester1',Cor_Name:'Data Science'}`]-(x:FLNode:dscor)
RETURN DISTINCT [x.Name_F,ds1.Cor_Node];
I was wondering if there is a way to do the following in a single query?
1) non_populated_models = PropertyPerson.select("property_people.id, count('items.recipient_person_id')").joins(:items).group('items.recipient_person_id, property_people.id')
2) populated_models = PropertyPerson.where(id: [non_populated_models])
Currently, the first group by query only returns the id, and count in the ProperyPerson object. Let's say there were 15 fields in the model and I didn't want to explicitly write them all out. Is there a way I can do this operation in a single query?
The join will work to limit the query to property_people with item and you you will get the extra column as an attr_reader.
people = PropertyPerson.select("property_people.*,
count('items.recipient_person_id') as items_count")
.joins(:items)
.group("property_people.id")
people.first.item_count
I'm using Rails to search through a SQLite table (for other reasons I can't use the standard database-model system) using a SELECT query like so:
info = ActiveRecord::Base.connection.execute("SELECT * FROM #{form_name} WHERE EmailAddress = \"#{user_em}\";")
This returns the correct values, but for some reason the output is in duplicate, the difference being the 2nd set doesn't have column titles in the hash, instead going from 0-[num columns]. For example:
{"id"=>1, "Timestamp"=>"2/27/2017 14:26:03", "EmailAddress"=>"-snip-", 0=>1, 1=>"2/27/2017 14:26:03", 2=>"-snip-"}
(I'll note the obvious- there's only one row in the table with that information in it)
While it's not exactly a fatal problem, I'm interested as to why it's doing so and if it's possible to prevent it. Thanks!
This allows you to read the values both by column index or column name:
id = row[0]
timestamp = row["Timestamp"]
I need to find a way to display all Vacancies from my Vacancy model except the ones that a user already applied for.
I keep the IDs of the vacancies a certain user applied for in a seperate model AppliedVacancies.
I was thinking something line the lines of:
#applied = AppliedVacancies.where(employee_id: current_employee)
#appliedvacancies_id = []
#applied.each do |appliedvacancy|
#appliedvacancies_id << appliedvacancy.id
end
#notyetappliedvacancies = Vacancy.where("id != ?", #appliedvacancy_id)
But it does not seem to like getting an array of IDs. How would I go about fixing this?
I get following error:
PG::DatatypeMismatch: ERROR: argument of WHERE must be type boolean, not type record
LINE 1: SELECT "vacancies".* FROM "vacancies" WHERE (id != 13,14)
^
: SELECT "vacancies".* FROM "vacancies" WHERE (id != 13,14)
This is purely an SQL problem.
You cannot use != to compare a value to a set of values. You need to use the IN operator.
#notyetappliedvacancies = Vacancy.where("id NOT IN (?)", #appliedvacancy_id)
As an aside, you can drastically improve the code you've written so far. You are needlessly instantiating complete ActiveRecord models for every record found in your applied_vacancies table, when all you need are the IDs.
A first pass at improvement would be to use pluck to skip the entire process and go straight to the list of IDs:
ids = AppliedVacancies.where(employee_id: current_employee).pluck(:id)
#notyetappliedvacancies = Vacancy.where("id NOT IN (?)", ids)
Next, you can go a step further and eliminate the first query all together (or rather, combine it with the last query as a sub-query) by leaving it as an AREL projection which can be subbed into the second query directly:
ids = AppliedVacancies.select(:id).where(employee_id: current_employee)
#notyetappliedvacancies = Vacancy.where("id NOT IN (?)",App)
This will generate a single query:
select * from vacancies where id not in (select id from applied_vacancies where employee_id = <value>)
Answer like #meagar, but Rails 4 way:
#notyetappliedvacancies = Vacancy.where.not(id: #appliedvacancy_id)
Hopefully this is a little clearer. I'm sorry but I'm very new to coding in general. I have multiple tables that I have to query in succession in order to get to the correct array that I need. The following logic for the query is as follows:
this gives me an array based upon the store :id
store = Stores.find(params[:id])
this gives me another array based upon the param .location found in the table store where that value equals the row ID in the table Departments
department = Departments.find(store.location)
I need to preform one last query but in order to do so I need to figure out which day of the meeting is needed. In order to do this I have to create the parameter day_of_meeting found in the table Stores. I try to call it from the array above and create a new variable. In the Table Departments, I there are params such as day_1, day_2 and so on. I need to be able to call something like department.day_1 or department.day_2. Thus, I'm trying to actually create the variable by join the words "department.day_" to the variable store.day_of_meeting which would equal some integer, creating department.day_1...
which_day = ["department.day_", store.day_of_meeting].join("")
This query finds uses the value found from the variable department.day_1 to query table Meeting to find the values in the corresponding row.
meeting = Meeting.find(which_day)
Does this make my problem any clearer to understand?
findmethod can only accept parameters like Meeting.find(1) or Meeting.find("1-xx").
so, what you need is Meeting.find(department.send("day_" + store.day_of_meeting.to_s))
Hope to help!