I have some Items with a foreign key to a parent Category. Is there an efficient way to query some Items and get fully populated Category objects?
The only approach I'm aware of is to use foreignAutoRefresh, or to refresh the Categories manually after the Item query, but this would result in an extra db hit for EACH Item object.
This can be done with a single JOIN, but if I do that is there any support for automatically building out the Category objects? Part (maybe all) of the problem is I don't fully understand the QueryBuilder's join functionality, but based on this answer it sounds like it doesn't do this:
Notice, however, that you can only get entities from the query builder
using this mechanism. If you want to get your two description fields
from different objects then you would have to still use a raw-query.
Alternatively, is there a way to refresh a collection of Categories in place with a single query, so that I can take the bare id-only Categories from the Item query and refresh them all?
In case it's of interest, the goal is to display these hierarchically in an ExpandableListView. Please let me know if I can provide any more info. I am comfortable throwing some SQL at it and populating Java objects myself if need be, but I'd rather stay within the framework if possible.
Related
Suppose, In my app I have a sqlite table that can contain at most 20 row. Each row has 2 column(id, name). Where I frequently need to search by Id to get Name. For this frequent need I have two solution:
Solution 1: Get rows in a arraylist<model> and then find name from array.
Solution 2: Every time search on sqlite table.
Now please give your opinion which one is better?
Remember again, I need this search in my recycleView item, so it call so frequently.
Thanks
I don't really get what is your real intent, but if your task is to search by id often, I would use
LongSparseArray<String> idsToNames; // or LongSparseArray<Model>
Which will map primitive long to Strings in a more memory-efficient way than Map and will have a better performance than ArrayList when searching.
The advantage over querying SQLite here is that you can do it in a blocking manner instead of having to query database on a background thread every time the lookup runs.
The disadvantage is that whenever data changes in SQLite, you will have to rebuild your idsToNames map. Also, if the number of entries in SQLite will eventually grow, you will end up in a large collection. So I would recommend this approach only if the updates to the database during this session will not happen, and if the data size is always predictable or fixed.
I am looking for some help to find a powerfull way to allow selection of different List items.
My case is that i have for exemple a List profiles, List teams ... and i'd like to have an autocomplete input that will show, for exemple if i type Al, all Teams and Profiles objects having there member variable name begining by Al.
The result would be that i could get from the activity, on submit click performed, a List & a List containing all the objects who have been selected through the autocomplete form.
Also i'd like that the list offered to the user that match the chars he typed show the name and a picture (facebook like tag selection).
Obviously i am not asking for some code but at least some guidelines from experienced Android devs who know what to do and not to do to create this kind of thing.
Thanks
Loader are one of the best way to filter list. You init a loader which take the String constraint used for filter, the each time the user type, you update the constraint and restart your Loader.
If I suppose that all your object are cached in a SQLite database you can use a CursorAdapter, Cursor and CursorLoader.
You create the needed CursorLoader by filter the query with the content of the EditText.
If you're not familiar with CursorLoader there is the AsyncTaskLoader, with this you won't have the need of DB and to code a provider which can accept raw query. Your object in ListA, ListB, etc must inherits of common class (hum... DataThing maybe :-)), you concatenate the objects in a list then you can filter the list : What is the best way to filter a Java Collection?
That's for the data filtering. Now in order to display the data the way you want, you can display of list below the EditText field or create a custom component if you want a more advanced look.
I have in my db 2 table with a many to many relationship.
TAB_ARTICLES: {_ID, TITLE, BODY, DATE}
TAB_TAG: {_ID, NAME, COLOR, DATE}
TAB_ART_TAG: {_ID, ARTICLE_ID, TAG_ID}
I need to populate a ListView, one row for article and in every row I need to have a TextView for every label linked to that article. Like the following image
I think 2 solutions.
a. I use a CursorAdapter with a cursor made only on TAB_ARTICLE and than in every row I do a query to join the other 2 tables looking for all tags related at this article. This solution require a lot of db accesses.
b. I realize a temporary table
TABLE_TEMP: {ARTICLE_TITLE, ARTICLE_BODY, ARTICLE_DATE, TAG1_NAME, TAG1_COLOR, TAG2_NAME, TAG2_COLOR, ...}
and I use a query on this table as cursor for custom adapter. This solution use more space and have a limitation on possible displayed tags due to table columns.
Are there other ways?
Well, actually, it's a multicriterion thing: time, space, updates, search, etc. So there's no single recipe. It's very probable, however, that multiple queries will bog down scrolling. Worse, on some devices only. A temporary table may or may not be OK depending on the overall size of your data. And you may want to keep this redundant table in sync with the main one, making simultaneous updates to both.
One of the simplest trade-offs could be adding a redundant TEXT/CLOB column with the tag data (XML, JSON, other markup/separated format) to TAB_ARTICLES and keeping it in sync with your detail data. By the way, you will really need the M:M schema only if your queries substantiate that. Otherwise, the single table would suffice.
Again, I'd list and evaluate all the criteria first and decide what dimensions really need to be scalable and simplify the rest.
I'm trying to think of how to get around this problem. I have an ORMlite object that can belong to multiple Categories; I'm using another table (i.e. a ForeignCollection) to track many-to-many connections between my objects and categories.
The problem is if I update the object with changed categories, the new categories are added, but old ones are not removed.
In the JavaDoc for the update method of DAO I see this text:
NOTE: Typically this will not save changes made to foreign objects or
to foreign collections.
My question is about the use of the word "typically." Does this mean that there IS a way through some sort of setting to make sure that updates update related foreign objects/collections?
Or should I read the sentence as if "typically" was not there, assume there is no automatic method, and that I need to run extra queries on committing each object to delete old categories?
The problem is if I update the object with changed categories, the new categories are added, but old ones are not removed.
So you have an object that has a foreign collection of categories:
#ForeignCollectionField
ForeignCollection<Category> categories;
If you run categories.add(category1) or categories.remove(category1), then the underlying collection should remove those from its associated table using a built-in DAO.
If you are changing the category list some other way then you are going to have to remove the Category entries by hand using the categoryDao directly.
... about the use of the word "typically." Does this mean that there IS a way through some sort of setting to make sure that updates update related foreign objects/collections?
Not sure why I left the word "typically" there. I think it was a blanket statement to take into account the various auto-create, auto-refresh, etc. field settings -- I'm not sure. In any case, I've removed it from the code base.
ORMLite has no way to know if foreign objects have been changed. It does not create magic proxy objects nor sessions so that it can tell when a foreign object has been updated. You have to be explicit about what you want updated when. The documentation on foreign collections is quite explicit about it.
OrmLite will not save objects to ForeignCollections automatically. You have to store and delete these objects yourself. Ormlite will retrieve the objects in the ForeignCollection automatically for you, provided you set the right parameters in the annotation.
Ormlite is "lite". It does ORM, but not completely. It's not JPA or Hibernate.
I solved this problem by adding the new Category to the table Categories directly, instead of adding a new category to the Object's foreignCollection.
This can be done by simply creating a category ado and adding a new element.
A newCategory.setObject(object) is needed in order to create the relation with the object.
Hope this helps.
this is more of a question of theory than anything else. I am writing an android app that uses a pre-packaged database. The purpose of the app is solely to search through this database and return values. Ill provide some abstract examples to illustrate my implementation and quandary. The user can search by: "Thing Name," and what I want returned to the user is values a, b, and c. I initially designed the database to have it all contained on a single sheet, and have column 1 be key_index, column 2 be name, column 3 be a, etc etc. When the user searches, the cursor will return the key_index, and then use that to pull values a b and c.
However, in my database "Thing alpha" can have a value a = 4 or a = 6. I do not want to repeat data in the database, i.e. have multiple rows with the same thing alpha, only separate "a" values. So what is the best way to organize the data given this situation? Do I keep all the "Thing Names" in a single sheet, and all the data separately. This is really a question of proper database design, which is definitely something foreign to me. Thanks for your help!
There's a thing called database normalization http://en.wikipedia.org/wiki/Database_normalization. You usually want to avoid redundancy and dependency in the DB entities using a corresponding design with surrogate keys and foreign keys and so on. Your "thing aplpha" looks like you want to have a many-to-many table like e.g. one or many songs belong/s to the same or different genres. You may want to create dictionary tables to hold your id,name pairs and have foreign keys referencing these tables. In your case it will be mostly a read-only DB so you might want to consider creating indexes with high FILLFACTOR percentage don't think sqlite allows it to do though. There're many ways to design the database. Everything depends on the purpose of DB. You can start with a design of your hardware like raids/file systems/db block sizes to match the F-System's block sizes in order to keep the I/O optimal and where to put your tablespaces/filegroups/indexes to balance the i/o load. The whole DB design theory/task is really a deep subject which is not to be underestimated nor is a matter of few sentences in the answer of stackoverflow. :)
without understanding your data better here is my guess at what you are looking for.
table: product
- _id
- name
table: attribute
- product_id
- a