I am upgrading my database to add another column. What I am trying to do is (after the column is added in onUpgrade) this method is called from the main activity for each table (3 were upgraded). The method is supposed to replace all of the blanks in the new column with "1".
The code runs fine, stepping through, boolean test is true every time but when I open the table to view the data, the entire column is blank. The weird part is, my rowId numbers are incrementing every time. It starts out with 3 rows with rowIds of 1,2,3 respectively. After my code runs once, they now have rowIds of 4,5,6 respectively.
Can anyone help me out? KEY_ROWID is just my auto rowId number. KEY_MODE is just "mode" for column title. If I run through debugging it, the three rows I have show up in the code (it runs through the while loop 3 times).
public void checkBlanks(String table) {
Cursor cursor = mDb.query(table, new String[] {KEY_ROWID, KEY_MODE}, null, null, null, null, null);
while (cursor.moveToNext()) {
int modeCol = cursor.getColumnIndexOrThrow(KEY_MODE);
if (cursor.isNull(modeCol)) {
int rowId = cursor.getInt(cursor.getColumnIndexOrThrow(KEY_ROWID));
ContentValues args = new ContentValues();
args.put(KEY_MODE, 1); // replace the blank space with a "1"
boolean test = mDb.update(table, args, KEY_ROWID + "=" + rowId, null) > 0;
}
}
cursor.close();
}
Instead of manually looping through the rows, why don't you just leverage the power of SQL and update ALL of the rows in one call? E.g.
mDb.execSQL("UPDATE " + table + " SET " + KEY_MODE + " = 1;");
Since it's so simple, you can do this right in your onUpgrade() method.
You could have done that much easier:
1.) During onUpgrade(): "add column newcolumn default 1". This would add a new column with all newcolumns containing 1.
2.) onUpgrade() is already run: update table set newcolumn=1: Without a WHERE clause the whole table is affected.
There's not need to walk thru all rows.
What you want to do requires an SELECT...FOR UPDATE OF/UPDATE...WHERE CURRENT OF. I didn't do that with SQLite, so I don't know if this is supported.
In your situation (onUpgrade is already run) use 2.)
Related
How should i get most recent added record from database, where COL_2 should == param that I pass into it.
I can get all records where COL_2 is equal to param with this code, but I need only recent one
public Cursor getRowsLast(String param) {
SQLiteDatabase db = helper.getWritableDatabase();
String[] COLS = new String[]{DatabaseHelper.COL_1,DatabaseHelper.COL_2, DatabaseHelper.COL_3,DatabaseHelper.COL_4};
String where = param;
Cursor c = db.query(true, DatabaseHelper.TABLE_NAME, COLS, DatabaseHelper.COL_2 + " = '" + where + "'", null, null, null, null, null);
if(c != null){
c.moveToFirst();
}
return c;
}
The most reliable way to get the most recent row in a table is to have a column defined in the table for the time of insert/update. Make sure this value is accurate at the time of insert/update, and create an index on it. You can then sort (descending) on this column to determine which one is the most recent - it will be the first row.
As the automatically generated ID values increase with every insert, the row with the highest ID will be the one that was inserted most recently. So add an 'order by _id desc' and the first row will be the most recently inserted one.
Note - this does not cover updates. If you need the row most recently inserted or updated, you'll have to use an additional timestamp column like Doug Stevenson suggested.
Sorry, I'm new. I have a table and need to get the column ID of the first min value of the table. The table is organized so the values keep decreasing until they get to 0 and all subsequent values are equal to zero.
It is possible for none of the values to be zero in which case Id need the last ID. It is important that I only have one return ID because of how I'm implementing it. This is the code I tried first but I'm getting an error.
I did not try to add the exception of there being no 0s here because I thought it might be easier to add an If statement in the implementation of the method I use.
The error I get confuses me because It seems like I can't use FIRST when I thought I could, but here it is:
android.database.sqlite.SQLiteException: no such function: FIRST (code
1): , while compiling: SELECT FIRST (_id) FROM graph WHERE bac = 0;
My code:
public int getWhereZero(){
int zero = 0;
SQLiteDatabase db = getReadableDatabase();
String query = "SELECT FIRST (" + COLUMN_ID
+ ") FROM " + TABLE_GRAPH
+" WHERE " + COLUMN_BAC
+ " = 0;";
Cursor cursor = db.rawQuery(query, null);
if(cursor != null){
cursor.moveToFirst();
zero = cursor.getInt(cursor.getColumnIndex(COLUMN_ID));
cursor.close();
}
return zero;
}
SQLite doesn't have a FIRST() function. However, you can limit the number of rows returned to one using LIMIT, so sorting by the desired order will get the row you need:
SELECT column_id FROM graph ORDER BY bac LIMIT 1;
Currently, I am using the following statement to create a table in an SQLite database on an Android device.
CREATE TABLE IF NOT EXISTS 'locations' (
'_id' INTEGER PRIMARY KEY AUTOINCREMENT, 'name' TEXT,
'latitude' REAL, 'longitude' REAL,
UNIQUE ( 'latitude', 'longitude' )
ON CONFLICT REPLACE );
The conflict-clause at the end causes that rows are dropped when new inserts are done that come with the same coordinates. The SQLite documentation contains further information about the conflict-clause.
Instead, I would like to keep the former rows and just update their columns. What is the most efficient way to do this in a Android/SQLite environment?
As a conflict-clause in the CREATE TABLE statement.
As an INSERT trigger.
As a conditional clause in the ContentProvider#insert method.
... any better you can think off
I would think it is more performant to handle such conflicts within the database. Also, I find it hard to rewrite the ContentProvider#insert method to consider the insert-update scenario. Here is code of the insert method:
public Uri insert(Uri uri, ContentValues values) {
final SQLiteDatabase db = mOpenHelper.getWritableDatabase();
long id = db.insert(DatabaseProperties.TABLE_NAME, null, values);
return ContentUris.withAppendedId(uri, id);
}
When data arrives from the backend all I do is inserting the data as follows.
getContentResolver.insert(CustomContract.Locations.CONTENT_URI, contentValues);
I have problems figuring out how to apply an alternative call to ContentProvider#update here. Additionally, this is not my favored solution anyways.
Edit:
#CommonsWare: I tried to implement your suggestion to use INSERT OR REPLACE. I came up with this ugly piece of code.
private static long insertOrReplace(SQLiteDatabase db, ContentValues values, String tableName) {
final String COMMA_SPACE = ", ";
StringBuilder columnsBuilder = new StringBuilder();
StringBuilder placeholdersBuilder = new StringBuilder();
List<Object> pureValues = new ArrayList<Object>(values.size());
Iterator<Entry<String, Object>> iterator = values.valueSet().iterator();
while (iterator.hasNext()) {
Entry<String, Object> pair = iterator.next();
String column = pair.getKey();
columnsBuilder.append(column).append(COMMA_SPACE);
placeholdersBuilder.append("?").append(COMMA_SPACE);
Object value = pair.getValue();
pureValues.add(value);
}
final String columns = columnsBuilder.substring(0, columnsBuilder.length() - COMMA_SPACE.length());
final String placeholders = placeholderBuilder.substring(0, placeholdersBuilder.length() - COMMA_SPACE.length());
db.execSQL("INSERT OR REPLACE INTO " + tableName + "(" + columns + ") VALUES (" + placeholders + ")", pureValues.toArray());
// The last insert id retrieved here is not safe. Some other inserts can happen inbetween.
Cursor cursor = db.rawQuery("SELECT * from SQLITE_SEQUENCE;", null);
long lastId = INVALID_LAST_ID;
if (cursor != null && cursor.getCount() > 0 && cursor.moveToFirst()) {
lastId = cursor.getLong(cursor.getColumnIndex("seq"));
}
cursor.close();
return lastId;
}
When I check the SQLite database, however, equal columns are still removed and inserted with new ids. I do not understand why this happens and thought the reason is my conflict-clause. But the documentation states the opposite.
The algorithm specified in the OR clause of an INSERT or UPDATE
overrides any algorithm specified in a CREATE TABLE. If no algorithm
is specified anywhere, the ABORT algorithm is used.
Another disadvantage of this attempt is that you loose the value of the id which is return by an insert statement. To compensate this, I finally found an option to ask for the last_insert_rowid. It is as explained in the posts of dtmilano and swiz. I am, however, not sure if this is safe since another insert can happen inbetween.
I can understand the perceived notion that it is best for performance to do all this logic in SQL, but perhaps the simplest (least code) solution is the best one in this case? Why not attempt the update first, and then use insertWithOnConflict() with CONFLICT_IGNORE to do the insert (if necessary) and get the row id you need:
public Uri insert(Uri uri, ContentValues values) {
final SQLiteDatabase db = mOpenHelper.getWritableDatabase();
String selection = "latitude=? AND longitude=?";
String[] selectionArgs = new String[] {values.getAsString("latitude"),
values.getAsString("longitude")};
//Do an update if the constraints match
db.update(DatabaseProperties.TABLE_NAME, values, selection, null);
//This will return the id of the newly inserted row if no conflict
//It will also return the offending row without modifying it if in conflict
long id = db.insertWithOnConflict(DatabaseProperties.TABLE_NAME, null, values, CONFLICT_IGNORE);
return ContentUris.withAppendedId(uri, id);
}
A simpler solution would be to check the return value of update() and only do the insert if the affected count was zero, but then there would be a case where you could not obtain the id of the existing row without an additional select. This form of insert will always return to you the correct id to pass back in the Uri, and won't modify the database more than necessary.
If you want to do a large number of these at once, you might look at the bulkInsert() method on your provider, where you can run multiple inserts inside a single transaction. In this case, since you don't need to return the id of the updated record, the "simpler" solution should work just fine:
public int bulkInsert(Uri uri, ContentValues[] values) {
final SQLiteDatabase db = mOpenHelper.getWritableDatabase();
String selection = "latitude=? AND longitude=?";
String[] selectionArgs = null;
int rowsAdded = 0;
long rowId;
db.beginTransaction();
try {
for (ContentValues cv : values) {
selectionArgs = new String[] {cv.getAsString("latitude"),
cv.getAsString("longitude")};
int affected = db.update(DatabaseProperties.TABLE_NAME,
cv, selection, selectionArgs);
if (affected == 0) {
rowId = db.insert(DatabaseProperties.TABLE_NAME, null, cv);
if (rowId > 0) rowsAdded++;
}
}
db.setTransactionSuccessful();
} catch (SQLException ex) {
Log.w(TAG, ex);
} finally {
db.endTransaction();
}
return rowsAdded;
}
In truth, the transaction code is what makes things faster by minimizing the number of times the database memory is written to the file, bulkInsert() just allows multiple ContentValues to be passed in with a single call to the provider.
One solution is to create a view for the locations table with a INSTEAD OF trigger on the view, then insert into the view. Here's what that would look like:
View:
CREATE VIEW locations_view AS SELECT * FROM locations;
Trigger:
CREATE TRIGGER update_location INSTEAD OF INSERT ON locations_view FOR EACH ROW
BEGIN
INSERT OR REPLACE INTO locations (_id, name, latitude, longitude) VALUES (
COALESCE(NEW._id,
(SELECT _id FROM locations WHERE latitude = NEW.latitude AND longitude = NEW.longitude)),
NEW.name,
NEW.latitude,
NEW.longitude
);
END;
Instead of inserting into the locations table, you insert into the locations_view view. The trigger will take care of providing the correct _id value by using the sub-select. If, for some reason, the insert already contains an _id the COALESCE will keep it and override an existing one in the table.
You'll probably want to check how much the sub-select affects performance and compare that to other possible changes you could make, but it does allow you keep this logic out of your code.
I tried some other solutions involving triggers on the table itself based on INSERT OR IGNORE, but it seems that BEFORE and AFTER triggers only trigger if it will actually insert into the table.
You might find this answer helpful, which is the basis for the trigger.
Edit: Due to BEFORE and AFTER triggers not firing when an insert is ignored (which could then have been updated instead), we need to rewrite the insert with an INSTEAD OF trigger. Unfortunately, those don't work with tables - we have to create a view to use it.
INSERT OR REPLACE works just like ON CONFLICT REPLACE. It will delete the row if the row with the unique column already exists and than it does an insert. It never does update.
I would recommend you stick with your current solution, you create table with ON CONFLICT clausule, but every time you insert a row and the constraint violation occurs, your new row will have new _id as origin row will be deleted.
Or you can create table without ON CONFLICT clausule and use INSERT OR REPLACE, you can use insertWithOnConflict() method for that, but it is available since API level 8, requires more coding and leads to the same solution as table with ON CONFLICT clausule.
If you still want to keep your origin row, it means you want to keep the same _id you will have to make two queries, first one for inserting a row, second to update a row if insertion failed (or vice versa). To preserve consistency, you have to execute queries in a transaction.
db.beginTransaction();
try {
long rowId = db.insert(table, null, values);
if (rowId == -1) {
// insertion failed
String whereClause = "latitude=? AND longitude=?";
String[] whereArgs = new String[] {values.getAsString("latitude"),
values.getAsString("longitude")};
db.update(table, values, whereClause, whereArgs);
// now you have to get rowId so you can return correct Uri from insert()
// method of your content provider, so another db.query() is required
}
db.setTransactionSuccessful();
} finally {
db.endTransaction();
}
Use insertWithOnConflict and set the last parameter (conflictAlgorithm) to CONFLICT_REPLACE.
Read more at the following links:
insertWithOnConflict documentation
CONFLICT_REPLACE flag
for me, none of the approaches are work if I don't have "_id"
you should first call update, if the affected rows are zero, then insert it with ignore:
String selection = MessageDetailTable.SMS_ID+" =?";
String[] selectionArgs = new String[] { String.valueOf(md.getSmsId())};
int affectedRows = db.update(MessageDetailTable.TABLE_NAME, values, selection,selectionArgs);
if(affectedRows<=0) {
long id = db.insertWithOnConflict(MessageDetailTable.TABLE_NAME, null, values, SQLiteDatabase.CONFLICT_IGNORE);
}
Use INSERT OR REPLACE.
This is the correct way to do it.
I have a database that is being filled by user defined EditTexts. None of the edit texts should allow empty fields. I know that I can check for this with a couple simple if-statements: if myEditText.getText().toString().equals("") // display error. However I would perfer to use this opportunity to brush up on my SQLite and error catching (as demonstrated in my add method). How would I go about altering the columns in the table below to NOT NULL and generating/catching an error when a user attempts to add/update with empty fields?
My database table:
db.execSQL("CREATE TABLE inventory (category TEXT, itemNum TEXT, quantity INTEGER, price REAL, image INTEGER, UNIQUE(category, itemNum) ON CONFLICT FAIL);");
My add method:
... fill ContentValues values
try{
db.getWritableDatabase().insertWithOnConflict(DatabaseHelper.TABLE_NAME, DatabaseHelper.CATEGORY, values, SQLiteDatabase.CONFLICT_FAIL);
fillItemNumbers();
}
catch(SQLiteConstraintException e)
{
Toast
.makeText(MyActivity.this, etItemNum.getText().toString() + " already exists in " + catSpinner.getSelectedItem().toString() +". Consider using Update.",Toast.LENGTH_LONG)
.show();
}
My update method:
... fill ContentValues values
String[] args = {catSpinner.getSelectedItem().toString(), etItemNum.getText().toString()};
int rowsAffected = db.getWritableDatabase().update(DatabaseHelper.TABLE_NAME, values, DatabaseHelper.CATEGORY + "=? AND " + DatabaseHelper.ITEM_NUMBER + "=?" , args);
UPDATE:
I did a little digging and came up with this:
db.execSQL("CREATE TABLE inventory (category TEXT NOT NULL, itemNum TEXT NOT NULL, quantity INTEGER NOT NULL, price REAL NOT NULL, image INTEGER NOT NULL, UNIQUE(category, itemNum) ON CONFLICT FAIL);");
Is this what I am looking for? If so, how can I use this to my advantage (see above)?
I am not sure if you can actually Alter Column Definition for table. I know you can Alter Table itself, like adding new Column to Table. You might need little trick to modify your database if there is lot of data in it that you want to preserve.
One way to it to create new table and try copying data to new table and afterwards remove old table and rename new Table. It's not most efficient way to do it but it'll get the job done though.
http://www.sqlite.org/lang_altertable.html
EDIT
Here you go
CREATE TABLE inventory (category TEXT not null, itemNum TEXT not null, quantity INTEGER not null, price REAL not null, image INTEGER not null, UNIQUE(category, itemNum) ON CONFLICT FAIL);
EDIT 2
Try this
CREATE TABLE inventory (category TEXT not null ON CONFLICT FAIL, itemNum TEXT not null ON CONFLICT FAIL, quantity INTEGER not null ON CONFLICT FAIL, price REAL not null ON CONFLICT FAIL, image INTEGER not null ON CONFLICT FAIL, UNIQUE(category, itemNum) ON CONFLICT FAIL);
All you need to do is set the columns to NOT NULL.
Then use
insertWithOnConflict(String table, String nullColumnHack, ContentValues initialValues, int conflictAlgorithm)
and
updateWithOnConflict(String table, ContentValues values, String whereClause, String[] whereArgs, int conflictAlgorithm)`
There are several constants you can use for the conflictAlgorithm, depending on exactly what you want to happen. If you want to simply not enter the data into the table, CONFLICT_IGNORE will do the trick. If you want a return code letting you know so you can act on it (let the user know) then you might want CONFLICT_FAIL.
See this for further information.
Hope this helps.
I have an issue with SQLite on android. Right now, I'm pulling a JSON object from a server, parsing it, and putting each sub-object in a Table with things such as the Name, Row_ID, unique ID, etc. using this code:
public void fillTable(Object[] detailedList){
for(int i=0;i<detailedList.length;++i){
Log.w("MyApp", "Creating Entry: " + Integer.toString(i));
String[] article = (String[]) detailedList[i];
createEntry(article[0], article[1], article[2], article[3], article[4], article[5]);
}
}
createEntry does what it sounds like. It takes 6 strings, and uses cv.put to make an entry. No problems.
When I try to order them however, via:
public String[] getAllTitles(int m){
Log.w("MyApp", "getTitle1");
String[] columns = new String[]{KEY_ROWID, KEY_URLID, KEY_URL, KEY_TITLE, KEY_TIME, KEY_TAGS, KEY_STATE};
Log.w("MyApp", "getTitle2");
Cursor c = ourDatabase.query(DATABASE_TABLENAME, columns, null, null, null, null, KEY_TIME);
Log.w("MyApp", "getTitle3");
String title[] = new String[m];
Log.w("MyApp", "getTitle4");
int i = 0;
int rowTitle = c.getColumnIndex(KEY_TITLE);
Log.w("MyApp", "getTitle5");
for(c.moveToFirst();i<m;c.moveToNext()){
title[i++] = c.getString(rowTitle);
Log.w("MyApp", "getTitle " + Integer.toString(i));
}
return title;
}
Each entry actually has many duplicates. I'm assuming as many duplicates as times I have synced. Is there any way to manually call the onUpgrade method, which drops the table and creates a new one, or a better way to clear out duplicates?
Secondary question, is there any way to order by reverse? I'm ordering by time now, and the oldest added entries are first (smallest number). Is there a reverse to that?
If you don't want duplicates in one column then create that column with the UNIQUE keyword. Your database will then check that you don't insert duplicates and you can even specify what should happen in that case. I guess this would be good for you:
CREATE TABLE mytable (
_id INTEGER PRIMARY KEY AUTOINCREMENT,
theone TEXT UNIQUE ON CONFLICT REPLACE
)
If you insert something into that table that already exists it will delete the row that already has that item and inserts your new row then. That also means that the replaced row gets a new _id (because _id is set to automatically grow - you must not insert that id yourself or it will not work)
Your second question: you can specify the direction of the order of if you append ASC (ascending) or DESC (descending). You want DESC probably.
Cursor c = ourDatabase.query(DATABASE_TABLENAME, columns, null, null, null, null, KEY_TIME + " DESC");