I have (among others) two domain classes:
class Course {
String name
...
}
class Round {
Course course
String startweek // e.g. '201504'
String endweek // e.g. '201534'
String applcode // e.g. 'DA542133'
...
}
Application codes may be issued at several occasions and are then concatenated with 'applcode's separated by blanks. As I am streaming and parsing large amount of data (in XML format) from different sources, I might stumble on the same data from several sources, so I look up the records in the database to see if I may discard the rest of the stream or not. This is possible as the outermost tag contains data stating the above declared attributes. I search the database using:
def c = Course.findByName(name);
def found =
Round.findByCourseAndStartweekAndEndweekAndApplcodeLike(c, sw, ew,'%'+appc+'%')
where the parameters are fairly obvious and which works well but I find these 'findByBlaAndBlablaAnd...' very long and not very readable. My aim here is to find some more readable and thereby more comprehensible method. I have started to read about Criteria and HQL but I think one example or two would help me on the way.
Edit after reading the pages on the link provided by #injecteer:
It was fairly simple to make out the query above. I have worse thing to figure out but the query in my example became with criteria:
def found = Round.createCriteria().get {
eq ('course', c)
eq ('startweek', sw)
eq ('endweek', ew)
like ('applcode', '%'+appc+'%')
};
Much easier to read and understand than the original question.
Related
I am wondering if it is possible to create an XmlProvider from the data provided by an SqlDataProvider.
Naively it would be something like this:
type sql = SqlDataProvider<...>
let xml =
query {
for item in sql.GetDataContext().Main.Items do
select item.XmlData
head
}
type xmlType = XmlProvider<xml>
Of course this fails because xml is not a literal.
I'm curious if this is possible.
The short answer is: Yes.
And then the ifs and buts:
Given that the returned xml is structured (as in: about equal each time) then providing an example which is a literal would be ok.
Then the data from the database could be parsed like:
let someXmlDataNowType = xmlType.Parse(xml)
This is probably not what you want or asked about, but then again the short answer is: No ;-)
If you have a lot of queries with different XML my take would have been to write some code to generate the different XML in some files and even possibly write the f# automagically...
I have been using parameters to query node indexes as such (using the rest api in java)-
final QueryResult<Map<String,Object>> result = engine.query("start nd=node:name_index(name={src}) return nd.age as age", MapUtil.map("src", "Susan");
However I haven't been able to get this to work for a collection of nodes/names. I have been trying something along the lines of-
final QueryResult<Map<String,Object>> result = engine.query("start nd=node:name_index(name={src}) return nd.age as age", MapUtil.map("src", Arrays.asList("Susan","Brian", "Ian"));
But it refuses to compile. I as wondering if there is something wrong in my syntax or that parameters are not designed to work in this context.
The name= syntax in the start is meant to do an index lookup on a property. It won't do an IN lookup. The way you can do this sort of lookup is like this (note it depends on Apache's StringUtils):
List<String> names = Arrays.asList("Susan","Brian", "Ian");
String luceneQuery = "name:("+StringUtils.join(names, ",")+")";
engine.query("start nd=node:name_index({luceneQuery}) return nd.age as age", MapUtil.map("luceneQuery", luceneQuery));
Just a note, this is the "legacy" index way of doing things. In 2.0 they've introduced label-based indexes, which work entirely differently.
Thanks a lot; though it would still only return a non empty answer when I added a space after the comma in line 2. I used-
String luceneQuery = "name:("+StringUtils.join(names, ", ")+")";
and it returned the age of one person. When I tried this:
String luceneQuery = "fs:(fs:"+ StringUtils.join(names, " OR fs:")+")";
it gave me all three ages. However, I am still unsure about whether this query will be able to leverage the usual advantages of parameters , i.e. will the engine be able to reuse the query and execution path the next time around (this time we may want to query for 4 names instead of 3)
I have two object, a room type and a reservation. Simplified they are:
class Room {
String description
int quantity
}
class Reservation {
String who
Room room
}
I want to query for all rooms along with the number of rooms available for each type. In SQL this does what I want:
select id, quantity, occupied, quantity-coalesce(occupied, 0) as available
from room left join(select room_id, count(room_id) as occupied from reservation)
on id = room_id;
I'm not getting anywhere trying to work out how to do this with HQL.
I'd appreciate any pointers since it seems like I'm missing something fairly fundamental in either HQL or GORM.
The problem here is your trying to represent fields that are not your domain classes like available and occupied. Trying to get HQL\GORM to do this can be a bit a little frustrating, but not impossible. I think you have a couple options here...
1.) Build your domain classes so that there easier to use. Maybe your Room needs to know about it's Reservations via a mapping table or, perhaps write what you want the code to look like and then adjust the design.
For example. Maybe you want your code to look like this...
RoomReservation.queryAllByRoomAndDateBetween(room, arrivalDate, departureDate);
Then you would implement it like this...
class RoomReservation{
...
def queryAllByRoomAndDateBetween(def room, Date arrivalDate, Date departureDate){
return RoomReservation.withCriteria {
eq('room', room)
and {
between('departureDate', arrivalDate, departureDate)
}
}
}
2.) My second thought is... It's okay to use the database for what it's good for. Sometimes using sql in you code is simply the most effective way to do something. Just do it in moderation and keep it centralized and unit tested. I don't suggest you use this approach because you query isn't that complex, but it is an option. I use stored procedures for things like 'dashboard view's' that query millions of objects for summary data.
class Room{
...
def queryReservations(){
def sql = new Sql(dataSoruce);
return sql.call("{call GetReservations(?)}", [this.id]) //<-- stored procedure.
}
}
I'm not sure how you can describe a left join with a subquery in HQL. INn any case you can easily execute raw SQL in grails too, if HQL is not expressive enough:
in your service, inject the dataSource and create a groovy.sql.Sql instance
def dataSource
[...]
def sql= new Sql(dataSource)
sql.eachRow("...."){row->
[...]
}
I know it's very annoying when people try to patronize you into their way of thinking when you ask a question, instead of answering your question or just shut up, but in my opinion, this query is sufficiently complex that I would create a concept for this number in my data structure, perhaps an Availability table associated to the Room, which would keep count not only of the quantity but also of the occupied value.
This is instead of computing it every time you need it.
Just my $.02 just ignore it if it annoys you.
I'm attempting to pull up all entities that have a name that doesn't partially match a given string.
MyEntity.findAllByNameNotLike('bad%')
This gives me the following error:
No such property: nameNot for class: MyEntity
Possible solutions: name" type="groovy.lang.MissingPropertyException">
I had a quick look at the criteria style but I can't seem to get that going either,
def results = MyEntity.withCritieria {
not(like('name', 'bad%'))
}
No signature of method: MyEntity.withCritieria() is applicable for argument types: (MyService$_doSomething_closure1)
Ideally I would like to be able to apply this restriction at the finder level as the database contains a large number of entities that I don't want to load up and then exclude for performance reasons.
[grails 1.3.1]
I've worked out how to do this using withCriteria, the not should have been a closure of its own.
def results = MyEntity.withCritieria {
not {
like('name', 'bad%'))
}
}
The problem I initially had using withCriteria was that I was trying to test this as a unit test, which works fine with the dynamic finders, but not with the criteria API (as far as I can tell).
(I'll leave this unanswered for a day to see if anyone has a better solution, otherwise I'll accept my answer)
I'm working on an application at the moment in ASP.NET MVC which has a number of look-up tables, all of the form
LookUp {
Id
Text
}
As you can see, this just maps the Id to a textual value. These are used for things such as Colours. I now have a number of these, currently 6 and probably soon to be more.
I'm trying to put together an API that can be used via AJAX to allow the user to add/list/remove values from these lookup tables, so for example I could have something like:
http://example.com/Attributes/Colours/[List/Add/Delete]
My current problem is that clearly, regardless of which lookup table I'm using, everything else happens exactly the same. So really there should be no repetition of code whatsoever.
I currently have a custom route which points to an 'AttributeController', which figures out the attribute/look-up table in question based upon the URL (ie http://example.com/Attributes/Colours/List would want the 'Colours' table). I pass the attribute (Colours - a string) and the operation (List/Add/Delete), as well as any other parameters required (say "Red" if I want to add red to the list) back to my repository where the actual work is performed.
Things start getting messy here, as at the moment I've resorted to doing a switch/case on the attribute string, which can then grab the Linq-to-Sql entity corresponding to the particular lookup table. I find this pretty dirty though as I find myself having to write the same operations on each of the look-up entities, ugh!
What I'd really like to do is have some sort of mapping, which I could simply pass in the attribute name and get out some form of generic lookup object, which I could perform the desired operations on without having to care about type.
Is there some way to do this to my Linq-To-Sql entities? I've tried making them implement a basic interface (IAttribute), which simply specifies the Id/Text properties, however doing things like this fails:
System.Data.Linq.Table<IAttribute> table = GetAttribute("Colours");
As I cannot convert System.Data.Linq.Table<Colour> to System.Data.Linq.Table<IAttribute>.
Is there a way to make these look-up tables 'generic'?
Apologies that this is a bit of a brain-dump. There's surely imformation missing here, so just let me know if you'd like any further details. Cheers!
You have 2 options.
Use Expression Trees to dynamically create your lambda expression
Use Dynamic LINQ as detailed on Scott Gu's blog
I've looked at both options and have successfully implemented Expression Trees as my preferred approach.
Here's an example function that i created: (NOT TESTED)
private static bool ValueExists<T>(String Value) where T : class
{
ParameterExpression pe = Expression.Parameter(typeof(T), "p");
Expression value = Expression.Equal(Expression.Property(pe, "ColumnName"), Expression.Constant(Value));
Expression<Func<T, bool>> predicate = Expression.Lambda<Func<T, bool>>(value, pe);
return MyDataContext.GetTable<T>().Where(predicate).Count() > 0;
}
Instead of using a switch statement, you can use a lookup dictionary. This is psuedocode-ish, but this is one way to get your table in question. You'll have to manually maintain the dictionary, but it should be much easier than a switch.
It looks like the DataContext.GetTable() method could be the answer to your problem. You can get a table if you know the type of the linq entity that you want to operate upon.
Dictionary<string, Type> lookupDict = new Dictionary<string, Type>
{
"Colour", typeof(MatchingLinqEntity)
...
}
Type entityType = lookupDict[AttributeFromRouteValue];
YourDataContext db = new YourDataContext();
var entityTable = db.GetTable(entityType);
var entity = entityTable.Single(x => x.Id == IdFromRouteValue);
// or whatever operations you need
db.SubmitChanges()
The Suteki Shop project has some very slick work in it. You could look into their implementation of IRepository<T> and IRepositoryResolver for a generic repository pattern. This really works well with an IoC container, but you could create them manually with reflection if the performance is acceptable. I'd use this route if you have or can add an IoC container to the project. You need to make sure your IoC container supports open generics if you go this route, but I'm pretty sure all the major players do.