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Nov 13, 2014 Dear Sir, Thank you for this application. It has saved my time a lot. I have one suggestion. The code generated the function names in capital letters like (setNAME) instead of that it should use camel casing like setName. Jul 27, 2007 I don't think there's any built-in way but you can create a custom function for it pretty easily. Are you using sqlite directly or a wrapper? Sam - We're Hiring! Seeking a passionate developer to join our team building products. Position is in the Washington D.C. Dec 19, 2014 SQLite – Auto-Increment / Auto Generate GUID David Kittell December 19, 2014 Recently was asked if it’s possible to create an auto-incrementing GUID in SQLite.
Saving data to a database is ideal for repeating or structured data,such as contact information. This page assumes that you arefamiliar with SQL databases in general and helps you get started withSQLite databases on Android. The APIs you'll need to use a databaseon Android are available in the android.database.sqlite package.
Caution: Although these APIs are powerful, they are fairly low-level and require a great deal of time and effort to use:
Android SQLite. Android SQLite is a very lightweight database which comes with Android OS. Android SQLite combines a clean SQL interface with a very small memory footprint and decent speed. For Android, SQLite is “baked into” the Android runtime, so every Android application can create its own SQLite databases. Mar 24, 2020 Auto increment attribute when specified on a column with a numeric data types, generates numbers sequentially whenever a new row is added into the database. The Auto increment is commonly used to generate primary keys. The defined data type on the Auto increment should be large enough to accommodate many records. Android comes in with built in SQLite database implementation. SQLite supports all the relational database features. In order to access this database, you don't need to establish any kind of connections for it like JDBC,ODBC e.t.c. Database - Package. The main package is android.database.sqlite that contains the classes to manage your own databases.
- There is no compile-time verification of raw SQL queries. As your data graph changes, you need to update the affected SQL queries manually. This process can be time consuming and error prone.
- You need to use lots of boilerplate code to convert between SQL queries and data objects.
For these reasons, we highly recommended using the Room Persistence Library as an abstraction layer for accessing information in your app's SQLite databases.
Define a schema and contract
One of the main principles of SQL databases is the schema: a formaldeclaration of how the database is organized. The schema is reflected in the SQLstatements that you use to create your database. You may find it helpful tocreate a companion class, known as a contract class, which explicitly specifiesthe layout of your schema in a systematic and self-documenting way.
A contract class is a container for constants that define names for URIs,tables, and columns. The contract class allows you to use the same constantsacross all the other classes in the same package. This lets you change a columnname in one place and have it propagate throughout your code.
A good way to organize a contract class is to put definitions that areglobal to your whole database in the root level of the class. Then create an innerclass for each table. Each inner class enumerates the corresponding table's columns.
Note: By implementing the BaseColumnsinterface, your inner class can inherit a primarykey field called _ID that some Android classes such as CursorAdapter expect it to have. It's not required, but this can help your databasework harmoniously with the Android framework.
For example, the following contract defines the table name and column names for asingle table representing an RSS feed:
Create a database using an SQL helper
Once you have defined how your database looks, you should implement methodsthat create and maintain the database and tables. Here are some typicalstatements that create and delete a table:
Just like files that you save on the device's internalstorage, Android stores your database in your app's private folder. Your data issecure, because by default this area is notaccessible to other apps or the user.
The SQLiteOpenHelper class contains a usefulset of APIs for managing your database.When you use this class to obtain references to your database, the systemperforms the potentiallylong-running operations of creating and updating the database only whenneeded and not during app startup. All you need to do is callgetWritableDatabase() orgetReadableDatabase().
Note: Because they can be long-running,be sure that you call getWritableDatabase() or getReadableDatabase() in a background thread,such as with AsyncTask or IntentService.
To use SQLiteOpenHelper, create a subclass thatoverrides the onCreate() andonUpgrade() callback methods. You mayalso want to implement theonDowngrade() oronOpen() methods,but they are not required.
For example, here's an implementation of SQLiteOpenHelper thatuses some of the commands shown above:
To access your database, instantiate your subclass ofSQLiteOpenHelper:
Put information into a database
Insert data into the database by passing a ContentValuesobject to the insert() method:
The first argument for insert()is simply the table name.
The second argument tells the framework what to do in the event that theContentValues is empty (i.e., you did notput any values).If you specify the name of a column, the framework inserts a row and setsthe value of that column to null. If you specify null, like in thiscode sample, the framework does not insert a row when there are no values.
The insert() methods returns the ID for thenewly created row, or it will return -1 if there was an error inserting the data. This can happenif you have a conflict with pre-existing data in the database.
Read information from a database
To read from a database, use the query() method, passing it your selection criteria and desired columns.The method combines elements of insert()and update(), except the column listdefines the data you want to fetch (the 'projection'), rather than the data to insert. The resultsof the query are returned to you in a Cursor object.
The third and fourth arguments (selection and selectionArgs) arecombined to create a WHERE clause. Because the arguments are provided separately from the selectionquery, they are escaped before being combined. This makes your selection statements immune to SQLinjection. For more detail about all arguments, see thequery() reference.
To look at a row in the cursor, use one of the Cursor movemethods, which you must always call before you begin reading values. Since the cursor starts atposition -1, calling moveToNext() places the 'read position' on thefirst entry in the results and returns whether or not the cursor is already past the last entry inthe result set. For each row, you can read a column's value by calling one of theCursor get methods, such as getString() or getLong(). For each of the get methods,you must pass the index position of the column you desire, which you can get by callinggetColumnIndex() orgetColumnIndexOrThrow(). When finishediterating through results, call close() on the cursorto release its resources.For example, the following shows how to get all the item IDs stored in a cursorand add them to a list:
Delete information from a database
To delete rows from a table, you need to provide selection criteria thatidentify the rows to the delete() method. Themechanism works the same as the selection arguments to thequery() method. It divides theselection specification into a selection clause and selection arguments. Theclause defines the columns to look at, and also allows you to combine columntests. The arguments are values to test against that are bound into the clause.Because the result isn't handled the same as a regular SQL statement, it isimmune to SQL injection.
The return value for the delete() methodindicates the number of rows that were deleted from the database.
Update a database
When you need to modify a subset of your database values, use theupdate() method.
Updating the table combines the ContentValues syntax ofinsert() with the WHERE syntaxof delete().
The return value of the update() method isthe number of rows affected in the database.
Persisting database connection
Since getWritableDatabase()and getReadableDatabase() areexpensive to call when the database is closed, you should leave your database connectionopen for as long as you possibly need to access it. Typically, it is optimal to close the databasein the onDestroy() of the calling Activity.
Debug your database
The Android SDK includes a sqlite3 shell tool that allows you to browsetable contents, run SQL commands, and perform other useful functions on SQLitedatabases. For more information, see how to how to issue shell commands.
The SQLite.NET library that Xamarin recommends is a very basic ORM thatlets you easily store and retrieve objects in the local SQLite databaseon an Android device. ORM stands for Object Relational Mapping – anAPI that lets you save and retrieve 'objects' from a databasewithout writing SQL statements.
To include the SQLite.NET library in a Xamarin app, add the following NuGet package to your project:
- Package Name: sqlite-net-pcl
- Author: Frank A. Krueger
- Id: sqlite-net-pcl
- Url:nuget.org/packages/sqlite-net-pcl
Tip
There are a number of different SQLite packages available – be sure to choose the correct one (it might not be the top result in search).
Once you have the SQLite.NET library available, follow these three steps to use it to access a database:
Add a using statement – Add the following statement to the C#files where data access is required:
Create a Blank Database – A database reference can becreated by passing the file path the SQLiteConnection classconstructor. You do not need to check if the file already exists– it will automatically be created if required, otherwise theexisting database file will be opened. The
dbPathvariable shouldbe determined according the rules discussed earlier in thisdocument:Save Data – Once you have created a SQLiteConnectionobject, database commands are executed by calling its methods, suchas CreateTable and Insert like this:
Retrieve Data – To retrieve an object (or a list ofobjects) use the following syntax:
Basic Data Access Sample
The DataAccess_Basic sample code for this document looks like thiswhen running on Android. The code illustrates how to perform simpleSQLite.NET operations and shows the results in as text in theapplication's main window.
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The following code sample shows an entire database interaction usingthe SQLite.NET library to encapsulate the underlying database access.It shows:
Creating the database file
Inserting some data by creating objects and then saving them
Querying the data
You'll need to include these namespaces:
The last one requires that you have added SQLite to your project. Notethat the SQLite database table is defined by adding attributes to aclass (the Stock class) rather than a CREATE TABLE command.
Using the [Table] attribute without specifying a table name parameterwill cause the underlying database table to have the same name as theclass (in this case, 'Stock'). The actual table name is importantif you write SQL queries directly against the database rather than usethe ORM data access methods. Similarly the [Column('_id')] attributeis optional, and if absent a column will be added to the table with thesame name as the property in the class.
SQLite Attributes
Common attributes that you can apply to your classes to control howthey are stored in the underlying database include:
[PrimaryKey] – This attribute can be applied to aninteger property to force it to be the underlying table's primarykey. Composite primary keys are not supported.
[AutoIncrement] – This attribute will cause an integerproperty's value to be auto-increment for each new object insertedinto the database
[Column(name)] – The
nameparametersets the underlying database column's name.[Table(name)]/python-quick-generate-rsa-key-pair.html. – Marks the class as being able to bestored in an underlying SQLite table with the name specified.
[MaxLength(value)] – Restrict the length of a textproperty, when a database insert is attempted. Consuming codeshould validate this prior to inserting the object as thisattribute is only 'checked' when a database insert or updateoperation is attempted.
[Ignore] – Causes SQLite.NET to ignore this property.This is particularly useful for properties that have a type thatcannot be stored in the database, or properties that modelcollections that cannot be resolved automatically by SQLite.
[Unique] – Ensures that the values in the underlyingdatabase column are unique.
Most of these attributes are optional. You should always specify an integerprimary key so that selection and deletion queries can be performedefficiently on your data.
More Complex Queries
The following methods on SQLiteConnection can be used to perform other data operations:
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Insert – Adds a new object to the database.
Get<T> – Attempts to retrieve an object using theprimary key.
Table<T> – Returns all the objects in the table.
Delete – Deletes an object using its primary key.
Query<T> – Perform an SQL query that returns a number ofrows (as objects).
Execute – Use this method (and not
Query) when youdon't expect rows back from the SQL (such as INSERT, UPDATE andDELETE instructions).
Getting an object by the primary key
SQLite.Net provides the Get method to retrieve a single object based on its primary key.
Selecting an object using Linq
Methods that return collections support IEnumerable<T> so you can useLinq to query or sort the contents of a table. The following code showsan example using Linq to filter out all entries that begin with theletter 'A':
Selecting an object using SQL
Even though SQLite.Net can provide object-based access to your data,sometimes you might need to do a more complex query than Linq allows(or you may need faster performance). You can use SQL commands with theQuery method, as shown here:
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Note
When writing SQL statements directly you create adependency on the names of tables and columns in your database, whichhave been generated from your classes and their attributes. If youchange those names in your code you must remember to update anymanually written SQL statements.
Deleting an object
The primary key is used to delete the row, as shown here:
You can check the rowcount to confirm how many rows were affected(deleted in this case).
Using SQLite.NET with Multiple Threads
SQLite supports three different threading modes: Single-thread,Multi-thread, and Serialized. If you want to access the databasefrom multiple threads without any restrictions, you can configureSQLite to use the Serialized threading mode. It's important to setthis mode early in your application (for example, at the beginning ofthe OnCreate method).
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To change the threading mode, call SqliteConnection.SetConfig. Forexample, this line of code configures SQLite for Serialized mode:
The Android version of SQLite has a limitation that requires a few moresteps. If the call to SqliteConnection.SetConfig produces a SQLiteexception such as library used incorrectly, then you must use thefollowing workaround:
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Link to the native libsqlite.so library so that the
sqlite3_shutdownandsqlite3_initializeAPIs are madeavailable to the app:At the very beginning of the
OnCreatemethod, add this codeto shutdown SQLite, configure it for Serialized mode, andreinitialize SQLite:
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This workaround also works for the Mono.Data.Sqlite library. For moreinformation about SQLite and multi-threading, seeSQLite and Multiple Threads.