Here is my current SQLite table:
CREATE TABLE formula (_id INTEGER PRIMARY KEY AUTOINCREMENT,suggest_text_1 TEXT,formula TEXT,category TEXT);
I want to integrate search suggestions in an Android app, but I need a SUGGEST_COLUMN_INTENT_DATA_ID and I want my _id to represent it. But I also need a _id for the content provider. So is there a way where I could have SUGGEST_COLUMN_INTENT_DATA_ID and store the current and future values of _id in it? Would I use an alias?
Would I use an alias?
This is possible but it depends on your exact requirements. See my answer to this question to see if this applies to you. Android: column '_id' does not exist problem
Related
I have two tables that I have to fill in after scanning a NFC tag.
SCAN:
-IdScan
-Data
-Date
-Geolocation
-GEOLOCATION:
-Latitude
-Longitude
-Country
-PostalCode
-etc.
My question is : how to link these two tables ?
When I insert a new scan into Scan table, I'd like to create a link between Scan's location field and table LOCATION
I heard about foreign key but I don't know if it's useful in this case...
I am assuming (Geolocation) in SCAN table has the values Latitude and Longitude. Please refer to this link(though it's PostgreSQL, concepts should be applicable to any RDBMS too like sqlite.
DDL Constraints for Foreign Key
TL;DR: A foreign key constraint specifies that the values in a column (or a group of columns) must match the values appearing in some row of another table. We say this maintains the referential integrity between two related tables.
So in case you want to make (Geolocation) as Foreign Key - You must find a Primary key in Geolocation table so may be adding a date and making (date,lat,lon) as a composite primary key would make it a fit for referential integrity.
I am new to Android programming and I have made a few simple apps which use SQLite to store user's data. Now I am working on a little more complex app in which I need to implement many-to-many relationship among the tables.
So basically, I have three layers (3 Tables) that would be connected to each other and I can't find a good tutorial or any documentation on how to do it. I've spent weeks on researching this. I also looked into realm-database but it's complicated for many-to-many table setup.
So is there any easier solution to this for a beginner? Or is there another tool that I can use to accomplish my task. Any suggestions would be helpful. Thank you :)
Your example isn't a many to many relationship. It's a one to many, each country can only exist in one continent and each state in only one country.
You can get the structure you want by adding a reference to the parent type's ID.
CREATE TABLE continent (
_id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT,
name TEXT NOT NULL
)
CREATE TABLE country (
_id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT,
continentId INTEGER NOT NULL,
name TEXT NOT NULL,
FOREIGN KEY continentId REFERENCES continent(_id)
)
CREATE TABLE state (
_id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT,
countryId INTEGER NOT NULL,
name TEXT NOT NULL,
FOREIGN KEY countryId REFERENCES country(_id)
)
To select all the countries on a continent, just ask SQL using the correct ID.
SELECT *
FROM country
WHERE continentId = ?
Or you can join them together.
SELECT *
FROM continent
JOIN country ON continent._id = country.continent
JOIN state ON country._id = state.countryId
You can do many-to-may relationships with SQLite. For the example shown you just need some XREF tables. For example (pseudocode):
Table CONTINENT(
ContinentID
,ContinentName
)
Table COUNTRY(
CountryID
,CountryName
)
Table CONTINENT_COUNTRY_XREF (
Continent_Country_XrefID
,ContinentID
,CountryID
)
Hope this helps.
Yes you can use Ultralite database from SAP. It supports joins as well.
More details here
http://scn.sap.com/community/developer-center/mobility-platform/blog/2012/08/23/how-to-open-an-ultralite-db-udb
To connect two tables in a many to many relationship, create a third table with three columns. The first column is just a standard is for the primary key. The other two columns are secondary keys into the two original tables. Googling " many to many relationship" will provide more details.
I have a database in which i have created one table with name "SectionDetails".
In this table i have set "id" as a primary key with AUTOINCREMENT property.And i am inserting my data into this table.
However, i came to the scenario where i need to check if record i am inserting is already present or not(if record is present then replace it with same values or skip it,And if record is not present then insert new one ).
But when i tried to insert record with same column values, it increases the primary key and insert the same row again instead of replacing.
So, my question is-
Does sqlite "insert or replace" works with AUTOINCREMENT primary key?
I am using following query:
insert or replace into SectionDetails(Name,Month,Title,Url)values('Deepak',"August","None","www.dd619.com")
here column "id" is not appearing because its a primary key with AUTOINCREMENT property.
You will need to add some unique constraints to your other columns to make this work and even then you will have your IDs change.
insert or replace is really an insert with on conflict replace conflict resolution strategy. That is, when the insert would violate some constraint, all conflicting rows are first deleted and the insert takes place only then. The autoincrement mechanism will then generate a new ID value for you.
For more information: http://www.sqlite.org/lang_conflict.html
Short answer: no it does not.
The "insert or replace" only works well when you also specify the primary key. With the autoincrement in a setup that you describe, this cannot work.
Probably the quickest way to do that is by creating a custom insert/update method for your use case.
Looking at this answer I was trying to work out how to actually create a table with a column that is just an alias for ROWID. I would like to do this as some android classes require a unique column named '_id' but i dont want that col to be a PRIMARY KEY. I cant use AUTO_INCREMENT on the col that not a PK either, so I would just like _id to be an alias. I know I could do that in the query but thats not practical for my situation. Any pointers? Is this even possible?
Thanks :)
EDIT: really i just want to be able to have my own PK but also have an id field for CursorAdapters to work correctly etc
EDIT: Looking at Do i have to use _ID as a SQlite primary key? and does it have to be an INT? (Android Dev) it suggests to do it in the query if my PK is a number type also, but what if its a TEXT col that im using for my PK? (sort of thinking aloud here) - I guess i could copy CursorAdaptor and just getString instead of a long for the _id col (plus, pass the name of the col to use as the PK in to cursor adapter, get rid of _id!) OR just add a alias for the ROWID as _id in the SELECT, feels a bit hacky though...
You may have a primary key that is completely independent of SQLite's built-in rowid.
Every row of every SQLite table has a 64-bit signed integer key that uniquely identifies the row within its table. This integer is usually called the "rowid". The rowid value can be accessed using one of the special case-independent names "rowid", "oid", or "rowid" in place of a column name.
You may formulate your query so that the built-in rowid is called _id for the benefit of the CursorAdaptor by prepending the hidden rowid column to your results:
select _rowid_ as _id, ...
The rowid is unique, but need not be the primary key. You can make the primary key anything you like in the CREATE TABLE statement.
TBH, I don't think that this is really feasible. You are required to have that kind of PK column (even though with a lot of hacking you could create some kind of workaround).
I would rather suggest to have the _id column as a technical PK and have an additional column as logical PK i.e. just a freely defined column with a unique constraint. Your program logic should then be able to simply use the logical PK for all operations. Of course this would require you to use custom queries for find operations etc. but that is usually more fitting anyways.
hth..
Can anyone tell me how to declare a composite primary key in Android 1.6 which includes an autoincrement _id column? I'm not sure of the syntax. I've ended up just enforcing it in Java when I try to add values (where registrationNumber + date has to be unique in the table):
Cursor fuelUpsCursor = getFuelUps(registrationNumber, date);
if(!fuelUpsCursor.moveToNext())
{
//add registrationNumber and date
}
I don't really need the _id column but it can make life tricky if tables don't have one.
Cheers,
Barry
Your question does not make much sense. Your subject line asks for a "composite foreign key", your first sentence asks for a "composite primary key" with an AUTOINCREMENT that your sample code then ignores.
I am going to interpret your question this way: You want an _ID INTEGER PRIMARY KEY AUTOINCREMENT column in your table to be able to use Android's CursorAdapter, but you want to also make sure that the combination of two other columns is unique.
In that case, I think that you want to use a UNIQUE constraint:
Multiple Unique Columns in SQLite
SQLite table constraint - unique on multiple columns
http://sqlite.org/lang_createtable.html