Will leaving a Cursor open cause later commands to fail? - android

I have an app with a SQLite database in it; after opening a Cursor to get some data with a query like:
SELECT * FROM table_name WHERE id=42;
is it necessary to close the cursor before running a command like this:
UPDATE table_name SET column = datetime('now') WHERE id=42;
that affects the rows in the open Cursor?

This should be easy enough to test yourself.
The UPDATE statement will run, but the data in your existing Cursor will be out-dated. The general rule is to close the Cursor when you are done with it and if you use Loaders existing Cursors should refresh when the source data changes.

No, you can open a cursor, execute some updates on the selected rows and close the cursor afterwards (before db.close()). Sample:
Cursor cursor = db.rawQuery("SELECT id, ...");
if (cursor != null && cursor.moveToFirst()) {
int id = cursor.getLong ("id");
ContentValues values = new ContentValues();
values.put("id", id +1000);
values.put("name", name);
db.update(DATABASE_TABLE, args, "id=" + id, null);
}
cursor.close();
Note: updates on selected tables will have no effect on the (values of the) opened cursor.

Related

unable to retrieve data of column from database

I am having a table named keywords in database.I want to retrieve data of alarm and location columns from this table and unable to retrieve them except for contact number.For now I am showing their values in a Toast but every time I run any query to show my alarm or location in Toast its empty.But my contact_number is always shown.Don't understand the cause of this problem .I have also checked my tables view and it is showing the values of alarm ,location in them.
Create Table keywords( contact_number text primary key , alarm text , location text )
and my insert function is
public boolean insertkeys (String alarm ,String location ,String contact){
SQLiteDatabase db = this.getWritableDatabase();
//ContentValues is a name value pair, used to insert or update values into database tables.
// ContentValues object will be passed to SQLiteDataBase objects insert() and update() functions.
// ContentValues contentValues = new ContentValues();
ContentValues contentValues = new ContentValues();
contentValues.put("alarm",alarm);
contentValues.put("location",location);
contentValues.put("contact_number",contact);
long ins = db.insert("keywords",null,contentValues);
long upd = db.update("keywords",contentValues,"contact_number = ?",new String[]{contact});
// db.close();
if(ins == -1 && upd == -1)
return false;
else
return true;
}
I am inserting plus updating my data every single time my save button is clicked.Can anyone here tell how can I write a query to retrieve data of these fields and set it to Toast or Edit text. I am new to Database and stuck here for about a week. Thanks in advance for help :)
You extract data via a SELECT query which is returned as a Cursor when using the Android SDK.
The Cursor is similar to a table in that it has a number of rows, each with a set number of columns as determined by what you select.
To get all rows the SELECT query would be along the lines of :-
`SELECT * FROM keywords`
To do this using the Android SDK you could use the SQLiteDatabase query convenience method e.g. for the above you could use :-
Cursor cursor = db.query("keywords",null,null,null,null,null,null);
check the links above for the values/parameters that can be passed and how they correlate with the SELECT statement.
You then traverse the returned cursor extracting the data, typically using the Cursor's move??? methods. Noting that most will return false if the move could not be made and also noting that the original position in the Cursor is before the first row
As such you could have a method that returns a Cursor as per :-
public Cursor getAllKeys(){
SQLiteDatabase db = this.getWritableDatabase();
return db.query("keywords",null,null,null,null,null,null);
}
You could then process all the rows using :-
Cursor csr = yourDBHelper.getAllKeys();
while (csr.moveToNext()) {
String current_contact_number = csr.getString(csr.getColumnIndex("contact_number");
String current_alarm = csr.getString(csr.getColumnIndex("alarm");
String current_location = csr.getString(csr.getColumnIndex("location"));
...... your code to Toast or use the retrieved values
}
csr.close(); //<<<<<<<<<< you should always close a Cursor when finished with it.
Additional
In regard to the comment :-
Cursor query which you have suggested I tried to make changes in it
like putting column and where clause but after that it returns me
nothing when I execute it.Could you tell me that query too.
The following could be a method to retrieve just the alarm according to a contact number.
public String getAlarmByContactNumber(String contactNumber){
String rv = "";
SQLiteDatabase db = this.getWritableDatabase();
Cursor csr = db.query(
"keywords", //<<<<<<<<<<<< the FROM clause (less the FROM keyword) typically the name of the table from which the data is to be extracted (but can include JOINS for example, for more complex queries)
new String[]{"alarm"}, //<<<<<<<<<< A String[] of the column names to be extracted (null equates to * which means all columns) (note can be more complex and include functions/sub queries)
"contact_number=?", //<<<<<<<<<< WHERE clause (less the WHERE keyword) note **?** are place holders for parameters passed as 4th argument
new String[]{contactNumber},
null, //<<<<<<<<<< GROUP BY clause (less the GROUP BY keywords)
null, //<<<<<<<<<< HAVING clause (less the HAVING keyword)
null //<<<<<<<<<< ORDER BY clause (less the ORDER BY keywords)
);
if (csr.moveToFirst()) {
rv = csr.getString(csr.getColumnIndex("alarm"));
}
csr.close();
return rv;
}
The above assumes that you would only have/want one alarm per contact number.
The above is in-principle code, it has not been run or tested and may therefore contain some minor errors.

Most recent added record into database

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.

Queries in SQLite

I have the following insert statement in my app which work.
Before the insert I want to first check the database if the value name does not exist in the name column.
If it does not exists I want to continue with the insert, else display an error message.
How do I incorporate it into my existing statement below?
public void insert(HashMap<String, String> queryValues){
SQLiteDatabase database = this.getWritableDatabase();
ContentValues values = new ContentValues();
Cursor c = database.query("SELECT * FROM user_details where" + "name=?", new String[] {values.put("name") });
if (c.getCount() > 0) {
// don't do it
return;
}
else {
values.put("name", queryValues.get("name"));
values.put("age", queryValues.get("age"));
database.insert("user", null, values);
}
database.close();
}
The correct way to do this is to add a unique constraint on the name field, and then use insertWithOnConflict() with a last argument of CONFLICT_FAIL. That's actually the default behavior. Your insert will fail if it would otherwise cause a constraint violation (insert() will return -1).
If you don't want to do that, there's no magic. Query your DB for a row with the given name field. If you are returned >0 rows, don't perform the insert.
Cursor c = db.query(..., "name=?", new String[] {theName}, ...);
if (c.getCount > 0) {
// don't do it
return;
}

Update singel cell of a row in an SQLite database on Android

I wont to update a single cell of a row in the database. However the row contains of 5 columns so and i would like to not passing all the other values as well as they should remain the same.
I have this code snippet:
Cursor cursor = db.query(STATION_TABLE, null, null, null, null, null, null);
//If the database already include some stations.
if(cursor.moveToFirst())
{
ContentValues stationValues = new ContentValues();
for(StopLocation station: stations)
{
stationValues.clear();
//The database already includes the station
if(cursor.getString(POS_STA_ID).equals(station.getId()))
{
values.put(KEY_STA_DISTANCE, "null");
db.update(STATION_TABLE, stationValues, KEY_STA_ID + "=?", new String[]{station.getId()});
}
The db.update method throws this exception:
java.lang.IllegalArgumentException: Empty values
Any ideas on how to solve this?
If I understand the question correctly and assuming you are always dealing with one row, there are two possible ways to approach this:
First:
Get the values of all fields in the entire row, and declare them as content values before updating:
ContentValues cv = new ContentValues();
cv.put("Field1","123");
cv.put("Field2","True")
Second:
Use execSQL() method:
String strSQL = "UPDATE your_table SET Field1 = foo WHERE POST_STA_ID = "+ station.getId();
myDataBase.execSQL(strSQL);

Sqlite open helper insert else update?

I want to insert data successfully
Here is my code:
public void insertData(String strTableName,
ArrayList<HashMap<String, String>> arrListproductdatabase) {
db = this.getWritableDatabase();
ContentValues cv = new ContentValues();
for (int i = 0; i < arrListproductdatabase.size(); i++) {
// cv.put(columnName, arrListOfRecord.get(i).get("name"));
cv.put(columnproductname,
arrListproductdatabase.get(i).get("product"));
cv.put(columnproductprice,
arrListproductdatabase.get(i).get("price"));
cv.put(columnproductquantity,
arrListproductdatabase.get(i).get("quantity"));
cv.put(columnproductid,
arrListproductdatabase.get(i).get("productID"));
cv.put(columnresturantID,
arrListproductdatabase.get(i).get("resturantID"));
db.insert(strTableName, null, cv);
}
I want that when I have to press add button again, that time it should check if the product is already inserted, and in that condition it should update and all.
I don't want to create any duplicate value.
Any help would be appreciated!
you can check for the distinct values in the db. please follow the link to have more details
android check duplicate values before inserting data into database
Set 'Product' field as unique key. So when duplicate value arrives from standard insert, it will simply return -1 and the error message will be swallowed.
You can control the behavior by using insertWithOnConflict (String table, String nullColumnHack, ContentValues initialValues, int conflictAlgorithm) where you also specify a conflict algorithm that can be of values:
CONFLICT_ABORT
CONFLICT_FAIL
CONFLICT_IGNORE
CONFLICT_REPLACE
CONFLICT_ROLLBACK
Check out the reference for descrption of the conflict resolution types.
There is also an updateWithOnConflict
You can do that like this :
public boolean checkProduct(String product){
// shold open database here
Cursor mCursor =
db.query(true, DATABASE_TABLE, null, "product='" + product+"'", null, null, null, null, null);
if(mCursor != null){
mCursor.close();
// shold close database here
return true;
}
// shold close database first here also
return false;
}
Hope this helped you.

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