I have three entities. Let's say Apple, Banana and Cactus. Apple have some properties(colour, flavour...) and a many-to-one relation with Banana by Banana_id. Banana have some properties(....) and a many-to-one relation to Apple by Apple_id. Entity Cactus - some properties, many-to-one relation to Banana by Banana_id.
So, if I begin writing the query needed...
SELECT A.banana
FROM Apple A
WHERE A.someAppleProperty = something
AND A.someOtherAppleProperty > something else
AND A.banana.someBananaProperty = something
How to write an inner join, or use some other approach, so I can include property from Cactus entity in the WHERE clause
Apologise for the way I describe my problem, if someone understand what I've got in mind and help it'll be great.
SELECT A.banana
FROM Apple A, Cactus C
WHERE A.someAppleProperty = something
AND A.someOtherAppleProperty > something else
AND A.banana.someBananaProperty = something
AND C.foo = 'bar'
AND C.banana = A.banana
Related
I can't figure out the right syntax to use when including several models and using AND or OR clauses.
For example, there Shop model that has_one relation with Address model and belongs_to with Country.
How for example add OR to the below query:
Shop.includes(:address, :country)
Trying like this:
Shop.includes(:address, :country).where('countries.code'=> 'FR').and('counties.updated_at > ?', Date.today.days_ago(7))
raises the error:
NoMethodError: undefined method `and' for #<Shop::ActiveRecord_Relation:0x00007fb90d0ea3f8>
I found this thread at SO, but in this case, I have to repeat the same where clause before each OR statement? - looks not so DRY :(
What am I missing ?
Don't kick yourself... you don't need to use and at all, just string another where in:
Shop.includes(:address, :country).where('countries.code'=> 'FR').where('counties.updated_at > ?', Date.today.days_ago(7))
There is a better solution if you need to add multiple OR clause to AND clause. To get around it, there is arel_table method that can be used as follows.
Let's say we have the following models
Shop -> has_one :address
Shop -> belongs_to :country
and we would like to find all the shops by country code and address updated_at or country updated_at should be greater then a date you pass in:
some_date = Date.today
countries = Country.arel_table
addresses = Address.arel_table
# creating a predicate using arel tables
multi_table_predicate = countries[:updated_at].gt(some_date).or(addresses[:updated_at].gt(some_date))
# building the query
shops = Shop.includes(:address, :country).where(countries: {code: 'FR'}).where(multi_table_predicate)
This will execute a LEFT OUTER JOIN and here is where clause:
WHERE "countries"."code" = $1 AND ("countries"."updated_at" > '2019-03-12' OR "addresses"."updated_at" > '2019-03-12')
Sure, you can chain more tables and multiply OR conditions if you want.
Hope this helps.
Ok, I feel really stupid for asking this, but it's driving me nuts and I can't figure it out. The docs say I should be able to use select AS in a Rails/ActiveRecord query. So:
d = Dvd.where(id: 1).select("title AS my_title")
Is a valid query and if I do a to_sql on it, it produces the expected SQL:
SELECT title AS my_title FROM `dvd` WHERE `dvd`.`id` = 1
However, d.my_title will give an error:
NoMethodError: undefined method `my_title' for #<ActiveRecord::Relation
I need to be able to use AS since the columns I want to retrieve from different joins have the same name so I can't access them the "regular" way and have to resort to using AS.
I also don't want to resort to using find_by_sql for future compatibility and a possible switch form Mysql to PostGresql.
Just to clarify, what I'm really trying to do is write this SQL in a Railsy way:
SELECT tracks.name AS track_name, artists.name AS artist_name, composers.name AS composer_name, duration
FROM `tracks_cds`
INNER JOIN `tracks` ON `tracks`.`id` = `tracks_cds`.`track_id`
INNER JOIN `artists` ON `artists`.`id` = `tracks_cds`.`artist_id`
INNER JOIN `composers` ON `composers`.`id` = `tracks_cds`.`composer_id`
WHERE cd_id = cd.id
The top example was just a simplification of the fact that SELECT AS will not give you an easy way to refer to custom fields which I find hard to believe.
ActiveRecord automatically creates getter and setter methods for attributes based on the column names in the database, so there will be none defined for my_title.
Regarding the same common names, why not just do this:
d = Dvd.where(id: 1).select("dvds.title")
You can write your sql query and then just pass into ActiveRecord's execute method
query = "SELECT title AS my_title FROM `dvd` WHERE `dvd`.`id` = 1"
result = ActiveRecord::Base.connection.execute(query)
I am trying to query data in CRM 2011 and I need to join an ActivityParty. I can't seem to find any good documentation on it. Has anyone done this before. This is my query so far:
var linqQuery = (from r in gServiceContext.CreateQuery("campaignresponse")
join c in gServiceContext.CreateQuery("contact") on ((EntityReference)r["customer"]).Id equals c["contactid"] into opp
join a in gServiceContext,CreateQuery("lead") on ((EntityReference)r["customer"]).Id equals c["leadid"] into opp
from o in opp.DefaultIfEmpty()
where ((EntityReference)r["new_distributorid"]).Id.Equals(lProfileProperty.PropertyValue) && ((OptionSetValue)r["new_distributorstatus"]).Equals("100000002")
select new
{ }
So if you look at the query what I am trying to do is join the contact Entity and the lead Entity to CamapaignResponse via the customer field and the customer field is an ActivityParty field. Any ideas on how to do this? Thanks!
I'm having a hard time figuring out how your query is supposed to work, but I can tell you that you'll have an easier time if you generate Linq entities using the SDK. Then, instead of
from r in gServiceContext.CreateQuery("campaignresponse") where ...
you can just write
gServiceContext.CampaignResponseSet
.Where(cr => cr.property == value)
.Select(cr => new {cr, cr.childObject});
and so forth. You'll get strong typing and IntelliSense, too.
My data structure is set up this way
A user takes a number of modules
A module contains a number of courses
Here's how the relationship looks like:
How do I get a list of courses the user takes?
The query I have now is:
var courses = (from ClassEnrollment enrolment in entities.ClassEnrollment
where enrolment.UserID == UserID
join Module module in entities.Module
on enrolment.ModuleID equals module.ID
select module.Course
).ToList();
However, this doesn't result in a list of courses, but rather a list of list of courses.
How can I flatten this query to a list of distinct courses?
According to your data structure screenshot, you have a one-to-many relationship between the ClassEnrollment and Module, as well as navigational property called Module. You also have a many-to-many relationship between Module and Course, but the navigational property should be called Courses. Given your code, you want something like this:
var courses = entities.
ClassEnrollment.
Where(e => e.UserID == UserID).
SelectMany(e => e.Module.Courses).
ToList();
Your question, however, mentions a user: A user takes a number of modules, How do I get a list of courses the user takes?. I don't see any User entity anywhere else, though, so it would be nice if you could clarify. Are you using LINQ-to-SQL, btw?
Something like this:
var courses = from ClassEnrollment enrolment in entities.ClassEnrollment
from module in entities.Module
where enrolment.ModuleID equals module.ID && enrolment.UserID equals UserID
select module.Course
Use SelectMany.
You can use
courses.SelectMany(c => c);
In your query you don't need explicitly specify the type for the range variables
Or you can join course to the query
var query = from enrolment in entities.ClassEnrollment
join module in entities.Module on enrolment.ModuleID equals module.ID
join course in entities.Course on module.CourseID equals course.ID
where enrolment.UserID == UserID
select course;
var course = query.ToList();
Here is the expression
x => x.stf_Category.CategoryID == categoryId
x refers to an Product Entity that contains a Category. I am trying to load all Products that match given categoryId.
In the db the Product table contains a Foreign Key reference to Category (via CategoryId).
Question: I think I am doing it wrong. Is there something else one has to do in EF4 to create a LINQ expression of this type?
Are there any good examples of EF4 Linq expressions out there? Specifically something that queries on the basis of related entities such as my problem ?
Thanks !
You're looking for the Include method.
var query = db.Products.Include("Categories");
This is commonly referred to as eager loading.
Entity Framework will 'infer' the JOIN constraint based on the mapping you have specified.
The "magic string" needs to match the Entity Set name on your EDMX.
Check out this post for more info.
EDIT
I'm a little confused as to whether you want the Products and Categories, or just the Products which have a specific Category ID.
If the latter, this is the way to go:
var query = from p in db.products
join c in db.categories
on p.CategoryId equals c.CategoryId
where c.CategoryId == someCategoryId
select p;
Keep in mind though, the above query is exactly the same result as your original query.
If p is a product, then p.Categories will look at the Navigational Property of your Product entity on the EDMX, in which case it will be your Category FK.
As long as you setup your Navigational properties right, p.Categories is fine.
If you are using EF4 and the association between Category and Product classes has been picked up and defined in your Model, then all products with a specific categoryID can be selected as simple as:
x => x.CategoryID == categoryID
You don't need to join nor an eager loading for that.