A simple Delphi wrapper for Sqlite 3

Most applications use a database, and there are many excellent database engines to choose from, both free and commercial. SQLite is a small C library that has several advantages. It is open source, free, cross-platform, fast, reliable, and well supported. I had a Delphi 7 application using Sqlite 2.0. There are various wrappers available for Delphi, and around 18 months ago I tried all the ones I could get my hands on. Although several of them were of good quality, I found myself running into bugs caused by the complexity of implementing Borland’s TDataset and related database components. Since I didn’t require databinding, I chose a wrapper that implemented very simple access to Sqlite – it was written by Ben Hochstrasser and amended by Pablo Pissanetzky. An advantage for me was that I could easily see what the wrapper did and make my own amendments. I actually made rather a lot of changes, adding basic transaction support and implementing a crude dataset based on a TList. Despite its simplicity, I found it effective and reliable.

The main author of Sqlite, Dr D Richard Hipp, has since released Sqlite 3.0. This adds some useful features, including BLOB support and the ability to create tables that support case-insensitive comparisons. I decided to update my wrapper for Sqlite 3.0. This meant changing the code from using SQLite’s callback interface to use Sqlite3_Prepare and Sqlite3_Step instead (see the description of the Sqlite C interface). Most of the code written by Ben and Pablo has now gone, which I say not to demean their efforts, but to emphasise their innocence. I’ve also had a go at adding BLOB support. The new wrapper is not yet extensively tested, but so far it is working well.

I’m now offering the wrapper for download. You’re welcome to use it, although naturally it comes with no warranty. I’d be grateful for any comments, bug reports or improvements, though I’d like to keep the wrapper simple. Note this is for Delphi 7, not Delphi .NET (though I’ve also used Sqlite with .NET – see here).

More about the wrapper

This wrapper has two units and three main classes. Sqlite3.pas has the external declarations for sqlite3.dll. I’ve included a binary build of sqlite3.dll, made with Visual C++ 2003. It should work with other builds, so you can upgrade to later versions of the DLL without making changes to the wrapper (unless the Sqlite API itself changes).

Sqlitetable3.pas implements three classes, ESqliteException, TSqliteDatabase and TSqliteTable. Currently TSqliteDatabase has the following methods:

GetTable: execute an SQL query and return a resultset as a TSqliteTable.

ExecSQL: execute an SQL query that does not return data.

UpdateBlob: Update a blob field with data from a TStream object.

BeginTransaction, Commit, Rollback: sends SQL statements for transaction support.

TableExists: Returns true if the specified table exists in the database.

There is also an IsTransactionOpen property.

TSqliteTable represents a resultset. It maintains no link to the source database, so it is disconnected: you can keep a TSqliteTable in memory after freeing the source TSqliteDatabase. When created it is set to the first row. Navigate the resultset using Next and Previous, until EOF is True. At BOF the resultset is on the first row, but at EOF there is no valid row. RowCount retrieves the number of rows, which may be zero. To retrieve data, first use FieldIndex to get the index number of a particular field. Then use the appropriate Field… method to get the value: FieldAsString, FieldAsInteger, FieldAsDouble, FieldAsBlob or FieldAsBlobText. For other datatypes such as Currency or TDateTime, you currently need to convert to String or one of the other types – I’m planning to add some more types soon. I’ve not tested the Blob functionality extensively. Since the entire resultset must fit in memory, be cautious about retrieving large resultsets or resultsets with large amounts of Blob data.

Currently the only way to determine if a field contains a null value is with the FieldIsNull method. The other methods return zero, false or empty strings for null values.

I will be publising a basic tutorial on using the wrapper in the UK magazine PC Plus. I will also keep this page up-to-date with the latest version.

Update 19 February 2005: I’ve updated the wrapper for Sqlite 3.1.2. This changes the way column names are returned, so I’ve added a call to set the Pragma full_column_names on. I’ve also amended the field type detection to use the actual type when the declared type is not available, and added the utility function TableExists. The test application now shows a possible way to load, save and display images in a Sqlite database.

Update 15 August 2005: Thanks to Lukas Gebauer who has made the wrapper compatible with Delphi 4+ and added some new methods. See the readme for details. I’ve also followed Lukas’s suggestion in removing FieldAsBool – he points out that it is not a natural sqlite3 type. If this causes problems for anyone, let me know. I’ve left the previous version available for download just in case. Finally, I’ve included a Visual C++ 2003 release build of Sqlite3 version 3.2.2.

Update 27 August 2007: Thanks to Marek Janáč who emailed me to say that the wrapper did not work with the latest Sqlite3 dll (3.4.2). The problem was that Sqlite now requires pathnames to be in UTF8 format when the path contains accented characters. I’ve made a small change to fix this. I’ve also included a new MSVC 6.0 build of the DLL. Finally, I’ve created a repository for the wrapper here:

http://www.itwriting.com/repos/sqlitewrapper/trunk

Update 16 October 2008: Quick update to get Delphi 2009 compatibility – not properly Unicode-enabled though, yet.

Update 4 February 2011: Added support for SQLite backup API. Updated DLL to Sqlite 3.7.5. Compiled with VC++ 10 but with static linking to avoid runtime dependencies.

Update 10 February 2011: Created new Unicode version. This has not been extensively tested, and requires Delphi 2009 or higher on Windows. Need to make this a single code base across all versions. Removed BindData method pending review for Unicode. Modified demo project to add simple navigation. You can download the Unicode version here.

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Links

Download the Simple Delphi Wrapper

Download the Unicode version

Sqlite home page

Other Sqlite wrappers including some for Delphi

My notes on using Sqlite 2 with Delphi, .NET and Java

My interview with the main author of Sqlite, Dr D Richard Hipp

166 thoughts on “A simple Delphi wrapper for Sqlite 3”

  1. @Allan

    That sounds odd. Are you inadvertently rolling back the changes? Is Vista writing a second copy of the file to another location, say in your virtual store?

    Tim

  2. Hi Tim,

    I am glad to have stumbled upon your wrapper. So far I have enjoyed using it, but have encountered a minor problem. Using Delphi 2009, it seems that TSQLiteDatabase.ExecSQL() and TSQLiteDatabase.GetTable() can not use SQL queries longer than 256 characters.

    For example, if I modify line 70 of uTestSqlite.pas in the included test application to:


    sSQL := 'INSERT INTO testtable(Name,OtherID,Number,Notes) VALUES ("Some Name",4,587.6594,"Here are some notes Here are some notes Here are some notes Here are some notes Here are some notes Here are some notes Here are some notes Here are some notes Here are some notes Here are some notes Here are some notes Here are some notes Here are some notes Here are some notes Here are some notes Here are some notes");';

    (i.e. adding an arbitrary amount of extra data to so that the statement surpasses 256 characters in length)

    I get this Debugger Exception Notification:

    Project TestSqlite.exe raised exception class ESQLiteException with message ‘Could not prepare SQL statement’.

    Any ideas on what may be causing this? I’ll definitely need to be using INSERT statements longer than 256 characters in my application.

    Thanks!

  3. @Mike sounds like a bug, though I’m surprised nobody else has shouted about this. I’ll check when I get a moment.

    Tim

  4. Hi Tim,

    After further investigation it looks more to be an IDE bug/configuration issue/oddity. If I break the string into two statements using concatenation, it works! Where as trying to assign a string more than 256 bytes at once results in the string being empty.

    For example, this would fix the code in my previous post:

    sSQL := 'INSERT INTO testtable(Name,OtherID,Number,Notes) VALUES ("Some Name",4,587.6594,"Here are some notes Here are some notes Here are some notes Here are some notes Here are some notes Here are some notes Here are some notes';
    sSQL := sSQL + ' Here are some notes Here are some notes Here are some notes Here are some notes Here are some notes Here are some notes Here are some notes Here are some notes Here are some notes");';

    Do you have this issue in your IDE? Any ideas on how to get around it in D2009?

    Thanks,

    Mike

  5. Hi Tim,

    I am happily using your wrapper. There is a bug in TSQLiteDatabase.Create() causing it to fail if there are unicode characters in the filename on D2007 and earlier.

    This line:
    utf8FileName := UTF8String(FileName);

    should be changed in:
    utf8FileName := UTF8Encode(FileName);

    That is because in D2007 and earlier UTF8String is just a typecast to a string. It does not convert anything.

  6. Hi, an update on the vista issue I experienced. My problem was my database file was located in the c:\program filesMYAPP directory beside the exe, and dll. To resolve, I had to change my files directory to the c:usersUSERAppDataLocalMYAPP directory. The problem seemed to be restricted permissions on the program files folders and files.

    My application also involved two executables working on the same sqlite database. I found that this caused lots of ‘Could not prepare SQL statement’ errors. to resolve this, I created a copy of the dll with a different name; so one dll for each exe. This resolved the issues and allowed me to have multiple connections to the same database.

    Hope this helps someone out there who may have the same problems.

    Regards,
    Allan.

  7. Hi!
    Please, show me example code, howto add UTF8 to base?
    For example, this string:
    ვეპხის ტყაოსანი შოთა რუსთაველი
    Insert into… does not work 🙁

  8. Hello, why you aren’t using the UTF8 features from the SQLite Database? Then you could use both Delphi “systems” and you can support the UTF8 Features with special characters.

    Like this:
    UTF8String in Database -> UTF8String in Wrapper -> The app now can convert it to Unicode/Wide/AnsiString. Or you support two functions to get the UTF8String “source” OR the converted “string”.

    Sincerely
    xZise

  9. @xZise @sergey there’s no good reason, I did the minimum to get it to compile in D2009 but haven’t added Unicode support. If anyone’s done this, let me have the code and I’ll post it. Otherwise it will have to wait until I have a spare moment.

    Tim

  10. I made some changes. Now I added a “Decode”-Option. You don’t create a table with “GetTable” (because then it is unsure who is the “owner” of the object -> better: GetTable gets a Tableobject and only “loads” the data). I also added the possibility to reuse a table (execute “QuerySQL”). And there is no “need” for next. You can get a value by Table.FieldAsString[Row, Column]. It is easy to implement the old “way”: You can execute the “FAS(ActualRow, ColAsParam)”.

    Next week I want to make it full/better Delphi 2009 compatible. By the way I now parse the Text from UTF8 to Ansi/Unicode (UTF-16) (depends on the used compiler). This is much easier to implement 😀
    So it looks like:
    App (Ansi/Unicode) -> Wrapper (Ansi/Unicode) -> Database (UTF-8)

    Sincerely
    xZise

  11. Hi Tim,
    I am having issues with updating a Blob as the updateBlob does not allow extra bindings to the sql query.

    I want to run the following query
    Update Sensors set last_pkt = ? where SerialNo = ?

    and have the bindings [stream,serialNo]

    Any suggestions on how I go about doing this?

    ps. I have looked at all the other wrappers and have found your wrapper the easiest one to implement so kudos to ya. 🙂

  12. Extending previous comment
    I have tried using the following
    UpdateBlob(format(‘Update Sensors set colour = “test”, last_pkt = ? where SerialNo = “%s”‘, [s.serial]),Stream);

    the where clause will work with ‘like’ but not with = so not sure what I am doing wrong.

  13. I have resolved my issue by using ExeSql with bindings passing a ? in the where clause

    I am kicking myself for such a stupid error.

    I do have another issue I am trying to store a Single value into the database but seem to be getting a invalid floating point error.

    would you know how to fix this issue?

  14. [clearing bindings feature]
    Hi Tim,
    I propose you add the [function SQLite3_ClearBindings(hStmt: TSqliteStmt): integer; cdecl; external SQLiteDLL name ‘sqlite3_clear_bindings’;] to SQLite3.pas
    What do you think?
    Best regards

  15. [BindSQL procedure]
    Hi Tim,
    [procedure TSQLiteDatabase.BindSQL(Query: TSQLiteQuery; const Index: Integer; const Value: String);] does not work properly when using TStringLists string pointing to ‘Value’.
    Eg:
    ..
    aSQLiteDatabase.BindSQL(aSQLiteQuery, 1, aStringList.ValueFromIndex[i]);
    ..
    aSQLiteDatabase.ExecSQL(SQLiteQuery);
    .. does not produce the expected result.

    To fix this, I’ve modified the BindSQL procedure: ptrDestructor -> Pointer(SQLITE_TRANSIENT) instead of ptrDestructor -> Pointer(SQLITE_STATIC)

    What do you think?

  16. @Didier

    I’ve tried to email you though I’m not 100% sure of the address – can you email me tim(at)itwriting.com if it does not arrive?

    Thanks for the suggestions.

    Tim

  17. Hi!
    Great wrapper!

    I’ve replaced my database from Firebird to SQLite and with this wrapper my code looks like much simpler now and it’s quarter of size then the original.
    Thanks a lot!

  18. Hi all,
    here are my changes, but there are many changes so most of the old code isn’t directly usable for this version. But it support “better” UTF Managment:
    http://xzise.xz.ohost.de/notvisible/sqlite.7z

    Added Features:
    – No Creation of tables as result
    – Decoded option
    – Working with the result as UTF8 string (So fully compatibility between SQLite and Ansi OR Unicode Versions of Delphi)
    – Value of a position (Col and Row) with no need of Next/First/Last or sth. else…
    – More features could be there but I forget them 😉

    ToDo:
    – Not urgent, but nice would be to read UTF16 strings instead of UTF8 string
    – Some function with unknown content aren’t translated to UTF8 😛

    Sincerely
    xZise

  19. Very good wrapper, thank you!
    I’m working with Delphi 2009.
    My program makes ExecSQL from thread, only one thread. But sometimes program are crashing with error:
    “Error executing SQL statement.
    Error [1]: SQL error or missing database.
    “COMMIT”: cannot commit – no transaction is active”
    But my code is:
    if sldb.IsTransactionOpen = true then sldb.Commit;

    I think, that var in module SQLiteTable3.pas – self.fInTrans is true but it must to be false.

    I am using the last wrapper from this site with no changes.
    Maybe, I should not do BeginTransaction?
    Thank you.

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