I used a code, generated from slick code generator.
My table has more than 22 columns, hence it uses HList
It generates 1 type and 1 function:
type AccountRow
def AccountRow(uuid: java.util.UUID, providerid: String, email: Option[String], ...):AccountRow
How do I write compiled insert code from generated code?
I tried this:
val insertAccountQueryCompiled = {
def q(uuid:Rep[UUID], providerId:Rep[String], email:Rep[Option[String]], ...) = Account += AccountRow(uuid, providerId, email, ...)
Compiled(q _)
}
I need to convert Rep[T] to T for AccountRow function to work. How do I do that?
Thank you
;TLDR; Not possible
Explanation
There are two levels of abstraction in Slick: Querys and DBIOActions.
When you're dealing with Querys, you have to access your schema definitions, and rows, Reps and, basically, it's very constrained as it's the closest level of abstraction to the actual DB you're using. A Rep refers to an hypothetical value in the database, not in your program.
Then you have DBIOActions, which are the next level... not just some definition of a query, but the execution of it. You usually get DBIOActions when getting information out of a query, like with the result method or (TADAN!) when inserting rows.
Inserts and Updates are not queries and so what you're trying to do is not possible. You're dealing with DBIOAction (the += method), and Query stuff (the Rep types). The only way to get a Rep inside a DBIOAction is by executing a Query and obtaining a DBIOAction and then composing both Actions using flatMap or for comprehensions (which is the same).
Related
Suppose I have two tables USER_GROUP and USER_GROUP_DATASOURCE. I have a classic relation where one userGroup can have multiple dataSources and one DataSource simply is a String.
Due to some reasons, I have a custom RecordMapper creating a Java UserGroup POJO. (Mainly compatibility with the other code in the codebase, always being explicit on whats happening). This mapper sometimes creates simply POJOs containing data only from the USER_GROUP table, sometimes also the left joined dataSources.
Currently, I am trying to write the Multiset query along with the custom record mapper. My query thus far looks like this:
List<UserGroup> = ctx
.select(
asterisk(),
multiset(select(USER_GROUP_DATASOURCE.DATASOURCE_ID)
.from(USER_GROUP_DATASOURCE)
.where(USER_GROUP.ID.eq(USER_GROUP_DATASOURCE.USER_GROUP_ID))
).as("datasources").convertFrom(r -> r.map(Record1::value1))
)
.from(USER_GROUP)
.where(condition)
.fetch(new UserGroupMapper()))
Now my question is: How to create the UserGroupMapper? I am stuck right here:
public class UserGroupMapper implements RecordMapper<Record, UserGroup> {
#Override
public UserGroup map(Record rec) {
UserGroup grp = new UserGroup(rec.getValue(USER_GROUP.ID),
rec.getValue(USER_GROUP.NAME),
rec.getValue(USER_GROUP.DESCRIPTION)
javaParseTags(USER_GROUP.TAGS)
);
// Convention: if we have an additional field "datasources", we assume it to be a list of dataSources to be filled in
if (rec.indexOf("datasources") >= 0) {
// How to make `rec.getValue` return my List<String>????
List<String> dataSources = ?????
grp.dataSources.addAll(dataSources);
}
}
My guess is to have something like List<String> dataSources = rec.getValue(..) where I pass in a Field<List<String>> but I have no clue how I could create such Field<List<String>> with something like DSL.field().
How to get a type safe reference to your field from your RecordMapper
There are mostly two ways to do this:
Keep a reference to your multiset() field definition somewhere, and reuse that. Keep in mind that every jOOQ query is a dynamic SQL query, so you can use this feature of jOOQ to assign arbitrary query fragments to local variables (or return them from methods), in order to improve code reuse
You can just raw type cast the value, and not care about type safety. It's always an option, evne if not the cleanest one.
How to improve your query
Unless you're re-using that RecordMapper several times for different types of queries, why not do use Java's type inference instead? The main reason why you're not getting type information in your output is because of your asterisk() usage. But what if you did this instead:
List<UserGroup> = ctx
.select(
USER_GROUP, // Instead of asterisk()
multiset(
select(USER_GROUP_DATASOURCE.DATASOURCE_ID)
.from(USER_GROUP_DATASOURCE)
.where(USER_GROUP.ID.eq(USER_GROUP_DATASOURCE.USER_GROUP_ID))
).as("datasources").convertFrom(r -> r.map(Record1::value1))
)
.from(USER_GROUP)
.where(condition)
.fetch(r -> {
UserGroupRecord ug = r.value1();
List<String> list = r.value2(); // Type information available now
// ...
})
There are other ways than the above, which is using jOOQ 3.17+'s support for Table as SelectField. E.g. in jOOQ 3.16+, you can use row(USER_GROUP.fields()).
The important part is that you avoid the asterisk() expression, which removes type safety. You could even convert the USER_GROUP to your UserGroup type using USER_GROUP.convertFrom(r -> ...) when you project it:
List<UserGroup> = ctx
.select(
USER_GROUP.convertFrom(r -> ...),
// ...
I'm new to Flask and have started designing a front end for an inventory management database using Flask-AppBuilder.
I have created several models and have have managed to display my sqlite data in tables using Flask-AppBuilder's views.
However, I don't seem to be able to find the equivalent of SQLite WHERE clause to filter or "restrict" column data. I've been reading a lot about sqlalchemy, filters, queries but this has left me more confused that anything else and the explanations seem to be extremely elaborate and complicated to do something which is extremely simple.
Assuming we reproduce the following SQLite query in Flask-AppBuilder:
SELECT Field_A
FROM Table_A
WHERE Field_A = 'some text'
with:
result = session.query(Table_A).filter_by(Field_A = 'some text').all()
Where does the above line of code go in my app?
Considering I have the following Class:
class Table_A(Model):
id = Column(Integer, primary_key=True)
Field_A = Column(String)
def __repr__(self):
return self
and View:
class Table_AView(ModelView):
datamodel = SQLAInterface(Table_AView)
label_columns = {'Field_A':'A'}
list_columns = ['Field_A']
After much digging flask-appbuilder uses it's own filterclass in order to enable you to filter your views.
All the classes are referenced here on GitHub:
Flask Filter Clases List
Also not the difference between FilterEqual and FilterEqualFunction here:
What is the difference between : FilterEqual and FilterEqualFunction?
For other customisation and first port of call of Flask-appbuilder go straight to the API Reference where you'll find a couple of examples of the filterclass in action.
In essence it is extremely simple. In your views.py code within the ModelView class you want to filter simply add base_filters = [['field_A', FilterEqual, 'abc']] like so:
`class Table_AView(ModelView):
datamodel = SQLAInterface(Table_AView)
label_columns = {'Field_A':'A'}
list_columns = ['Field_A']
base_filters = [['field_A', FilterEqual, 'abc']]`
This will only show the lines where the field_A variable is equal to abc.
Hope this helps someone as it took me nearly (sigh) two weeks to figure it out...
SQLALchemy is an ORM (Object-Relational Mapping), it mean that you dont have to deal with raw SQL, you will call a function that you "build" (by adding filters in your case). It will transparently generate an SQL query, execute it, and return the result as python objects.
I would suggest you to read closely at sqlalchemy documentation about filters again, especially filter_by :
http://docs.sqlalchemy.org/en/latest/orm/query.html#sqlalchemy.orm.query.Query.filter_by
It is the easiest way to apply a WHERE with sqlalchemy.
If you have declared correctly the model for Table_A, you should be able to use it so:
result = session.query(Table_A).filter_by(Field_A = 'some text').all()
Here session.query(Table_A).filter_by(Field_A = 'some text') will generate the SQL, and .all() will execute it.
suppose i have the following data in my database:
[1,2],[2,1],[1,3],[3,1]...
were the numbers represent the a and b values of the formula a*x+b
what i now want is a query that returns the difference to a given point x,y.
for example: the point [2,6] is given. i want my query to return
[1,2] = -2 (1*2+2=4 4-6=-2)
[2,1] = -1 (2*2+1=5 5-6=-1)
[1,3] = -1 (1*2+3=5 4-6=-1)
[3,1] = 1 (3*2+1=7 7-6=-1)
I know how to do this in SQL but the data is already in a couchdb. I'm quite new to the NoSQL world and was wondering if something like this would be possible in couchdb.
what you can do is to use the standard MapReduce functionality of CouchDB.
Map is function you put in a view, which finds your data. You can have various criteria how to locate the docs you need. Next, if you specify so in the query with reduce=true, a reduce function is executed on each document that matched the map condition. You can use JavaScript to perform various operations on the document's values.
In your case, the map can look something like this:
function(doc) {
if(doc.a && doc.b) {
emit(doc._id,[doc.a, doc.b]);
}
}
then, the reduce gets called, like this:
function(keys, values, rereduce) {
var res;
//do something with values...
return res;
}
In your case keys will be list of document ID's and values will be the array of your a & b fields.
When you call the MapReduce (depending what method you use to access the DB), you should specify reduce=true.
Good resources on MapReduce (and on Views, Sorting and List funtions) are:
http://guide.couchdb.org/draft/views.html
http://www.slideshare.net/okurow/couchdb-mapreduce-13321353
Another way to go is to use a list function on the Map result, if you want to output the result in HTML. A good reason to use List function is that you can pass arguments to it with querystring, in your case it may be the point for which you want to calculate distances.
For detailed description on List functions, have a look here:
http://guide.couchdb.org/draft/transforming.html
Hope this helps.
Pardon my newbieness but im trying to build a completely ad-hoc query builder using slick. From our API, I will get a list of strings that is representative of the table, as well as another list that represents the filter for the tables, munge then together to create a query. The hope is that I can take these and create the inner join. A similar example of what i'm trying to do would be JIRA's advanced query builder.
I've been trying to build it using reflection but I've come across so many blocking issues i'm wondering if this is even possible at all.
In code this is what I want to do:
def getTableQueryFor(tbl:String):TableQuery[_] = {
... a matcher that returns a tableQueries?
... i think the return type is incorrect b/c erasure?
}
def getJoinConditionFor:(tbl1:String, tbl2:String) => scala.slick.lifted.Column[Boolean] = (l:Coffees,r:Suppies) => {
...a matcher
}
Is the Following even possible?
val q1 = getTableQueryFor("coffee")
val q2 = getTableQueryFor("supply")
val q3 = q1.innerJoin.q2.on(getJoinCondition("coffee", "supply")
edit: Fixed grammar issue.
# student.rb
has_and_belongs_to_many :courses
# course.rb
has_and_belongs_to_many :students
I'm trying to create a scope in the students model that will check if they are enrolled in a course.
The best I've come up with is:
scope :unenrolled, where(Student.courses.count => 0)
But then I get the error message
undefined method `courses'
Anybody offer any suggestions?
Alright then. So here's your code:
scope :unenrolled, where(Student.courses.count => 0)
The first problem here is the thing that's causing the error: You're calling the instance method courses on the class Student. As the name implies, you can only call an instance method on an instance of a class, not on the class itself. For example:
jim = Student.find(123)
jims_courses = jim.courses
But here's the kicker: When you call scope you're in the class context, i.e. the code isn't inside an instance method, so it gets called when your model is first declared. There's no instance at that time so you can't just call courses like you would from within one of Student's instance methods.
But that's kind of moot since you've slightly misunderstood how where works. The argument(s) you give to where are supposed to be conditions that correspond to what you would put after WHERE in an SQL query. For example where(:eye_color => 'brown') will be turned into an SQL WHERE clause like WHERE eye_color = 'brown'. :eye_color => 'brown' is just a Hash with the key :eye_color whose value is 'brown'. Calling a function on the left side of => doesn't make sense unless the function returns the name of a column/attribute in your model that ActiveRecord will understand.
So now let's figure out what you should do. If you were writing an SQL query it would look something like this:
SELECT `students`.*, COUNT(`courses_students`.*) AS `courses_count`
FROM `students`
JOIN `courses_students` ON `students`.`id` = `courses_students`.`student_id`
WHERE `courses_count` = '0'
GROUP BY `courses_students`.`student_id`;
This translates roughly to an ActiveRecord query like this:
Student.joins(:courses). // AR automatically joins courses though courses_students
select('students., COUNT(courses.) AS courses_count').
where('courses_count = 0').
group('id')
And you can plunk that directly into your scope:
scope :unenrolled, joins(:courses).
select('students.*, COUNT(courses.*) AS courses_count').
where('courses_count = 0').
group('courses.course_id')
Note: These queries are a bit off-the-cuff and may require a bit of tweaking. The easiest way to build complicated ActiveRecord queries is by entering them directly into the Rails console until you get the results you want.
Hope that's helpful!