A Portable Class Library (PCL) for low-level (raw) access to SQLite
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README.md

SQLitePCL.raw

SQLitePCL.raw is a Portable Class Library (PCL) for low-level (raw) access to SQLite. License: Apache License v2.

TLDR

Add this package:

SQLitePCLRaw.bundle_e_sqlite3 

And call this function:

SQLitePCL.Batteries.Init()

Compatibility

SQLitePCL.raw should work just about anywhere you want it to, including:

  • Xamarin.Android
  • Xamarin.iOS
  • UWP
  • Windows Phone 8.1
  • .NET 4.5
  • .NET 4.0
  • .NET 3.5
  • Linux
  • MacOS
  • NetStandard 1.1
  • Windows Phone 8 (with limitations)
  • Windows Phone 8.1 Silverlight (with limitations)

(I have received a pull request for WatchOS support, but it's not merged yet.)

These packages should be fully compatible with NuGet 2.x or 3.x, either packages.config or project.json.

What's new in 1.0

In terms of the code, not much. But the builds and packaging have changed a lot.

At a very high level, this is the release that happened because Android N fouled everything up.

At a slightly-less-high level, the fixes and new features are:

  • All package names now begin with SQLitePCLRaw. For example, the main package is now called SQLitePCLRaw.core.
  • Support netstandard
  • Switch all the tests to xUnit.net
  • Fix problems with UWP apps failing validation
  • Support winsqlite3.dll (the one built-in to Windows 10)
  • Fix and refactor things where Android N broke my old assumptions
  • Provide an easier way for people to use custom sqlite3 builds
  • Improve my automated tests to test the nuget packaging, not just the code
  • Make the iOS sqlite builds compatible back to iOS 6
  • Be compatible with strong naming
  • sqlite3_threadsafe (#92)
  • Update e_sqlite3 (the sqlite builds which I bundle) to 3.14.1

New package names for release 1.0

With the release of version 1.0, all the nuget package ids are different. The are all prefixed with "SQLitePCLRaw.".

The main package is SQLitePCLRaw.core, previously called SQLitePCL.raw

Old packages ids

Before 1.0, the package ids were

  • SQLitePCL.raw
  • SQLitePCL.raw_basic
  • SQLitePCL.ugly
  • SQLitePCL.plugin.*
  • SQLitePCL.native.*
  • SQLitePCL.bundle*

All of these packages are being deprecated.

Note: Once a package (like sqlite-net-pcl, for example) has migrated to the 1.0 release, developers using that package may need to explicitly remove these old packages from their build.

Migrating to 1.0

Aside from the all new package ids, the 1.0 release contains some minor breaking changes to the way things get initialized. Migrating from previous versions will in some cases require an extra initialization call. The actual API for talking to SQLite has not changed.

SemVer

Starting with the 1.0 release, I will be attempting to follow SemVer for the verson numbers.

How the packaging works

The main assembly is SQLitePCLRaw.core. A PCL project would need to only take a dep on this one. All the other packages deal with initialization and the question of which instance of the native SQLite library is involved.

Many different native SQLite libraries

In some cases, apps use a SQLite library which is externally provided. In other cases, an instance of the SQLite library is bundled with the app.

  • On iOS, there is a SQLite library provided with the operating system, and apps are allowed to use it.

  • Android also has a SQLite library, and prior to Android N, apps were allowed to use it.

  • Recent versions of Windows 10 have a SQLite library.

  • In some cases, people want to use SQLCipher as their SQLite library.

  • Sometimes people want to compile and bundle their own custom SQLite library.

SQLitePCL.raw supports any of these cases.

Providers

In this context, a "provider" is the piece of code which tells SQLitePCL.raw which instance of the native code to use.

As of 1.0, the SQLitePCLRaw.core package contains no providers. This is the essence of how things have changed in the last few releases.

  • In 0.8.x and prior, the main package tried to contain all the providers that might be needed. But the package was getting enormous, and the use of funky MSBuild properties was a frustrating way to do configuration.

  • In 0.9.x, the main package contained one default provider as a fallback, and all the others were moved into packages named SQLitePCL.plugin.*. But this was problematic for certain UWP scenarios (which could not handle unused providers in the build), and Android N (where the so-called default provider is always the wrong thing to use).

  • In 1.0, the main package contains no providers, and requires that one be, er, provided.

More specifically, a "provider" is an implementation of the ISQLite3Provider interface. It is necessary to call SQLitePCL.raw.SetProvider() to initialize things.

All the various providers are in packages with ids of the form SQLitePCLRaw.provider.*.

Provider names

Providers are named for the exact string which is used for DllImport (pinvoke).

For example:

[DllImport("foo")]
public static extern int whatever();

This pinvoke will look for a library called "foo".

  • On Windows, that means "foo.dll".
  • On Unix, "libfoo.so"
  • On MacOS, "libfoo.dylib"

(The actual rules are more complicated than this.)

So, a provider where all the DllImport attributes were using "foo", would have "foo" in its package id and in its class name.

Included providers

SQLitePCL.raw includes the following providers:

  • "sqlite3" -- This matches the name of the system-provided SQLite on iOS (which is fine), and Android (which is not allowed). It also matches the name of the SQLite library provided by the extension SDKs in the Visual Studio gallery. And it matches the official name of builds provided at sqlite.org.

  • "sqlcipher" -- Intended to be used for SQLCipher builds with (what is assumed to be) the most common form of the library name.

  • "winsqlite3" -- Matches the name of the library provided by recent builds of Windows 10.

  • "e_sqlite3" -- This is the name of all SQLite builds provided as part of this project.

  • "custom_sqlite3" -- If you want to build your own SQLite library, give it this name and use this provider.

  • "sqlite3_xamarin" -- Matches the name of the SQLite library provided by Xamarin.Android for use with Mono.Data.Sqlite. This is only for situations where you need to use SQLitePCL.raw to work with the same SQLite instance as Mono.Data.Sqlite on Android.

SQLitePCLRaw.lib

A provider is the bridge between the core assembly and the native code, but the provider does not contain the native code itself.

In some cases (like "winsqlite3") this is because it does not need to. The provider is merely a bridge to a SQLite library instance which is known (or assumed) to be somewhere else.

But in cases where the app is going to be bundling the native code library, those bits need to make it into your build output somehow.

Packages with ids named "SQLitePCLRaw.lib.*" contain native code. This project distributes two kinds of these packages:

  • "sqlcipher" -- These are re-packaging of the SQLCipher builds maintained by Couchbase.

  • "e_sqlite3" -- These are builds of the SQLite library provided for the convenience of SQLitePCL.raw users. I try to keep them reasonably current with respect to SQLite itself (www.sqlite.org). The build configuration is the same for every platform, and includes full-text-search. If you are building an app on multiple platforms and you want to use the same recent version of SQLite on each platform, e_sqlite3 should be a good choice.

A trio of packages

So, using SQLitePCL.raw means you need to add two packages:

  • SQLitePCLRaw.core
  • SQLitePCLRaw.provider.whatever

And in many cases one of these as well:

  • SQLitePCLRaw.lib.whatever

And in your platform-specific code, you need to call:

SQLitePCL.raw.SetProvider(new SQLitePCL.SQLite3Provider_whatever());

But the word "whatever" is different on each platform. For example, on Android, using e_sqlite3, you need:

  • SQLitePCLRaw.core
  • SQLitePCLRaw.provider.e_sqlite3.android
  • SQLitePCLRaw.lib.e_sqlite3.android

and you need to call:

SQLitePCL.raw.SetProvider(new SQLitePCL.SQLite3Provider_e_sqlite3());

Bundles

To make things easier, SQLitePCL.raw includes "bundle" packages. These packages automatically bring in the right dependencies for each platform. They also provide a single Init() call that is the same for all platforms.

Think of a bundle as way of giving a "batteries included" experience.

So for example, SQLitePCLRaw.bundle_e_sqlite3 is a bundle that uses e_sqlite3 in all cases. Just add this package, and call:

SQLitePCL.Batteries.Init();

SQLitePCLRaw.bundle_green is a bundle that uses e_sqlite3 everywhere except iOS, where the system-provided SQLite is used.

SQLitePCLRaw.bundle_sqlcipher does not exist yet, but probably will soon.

The purpose of the bundles is to make things easier by taking away flexibility and control. You don't have to use them.

e_sqlite3 builds for Windows

For Windows, I have a lib.e_sqlite3 package for each platform toolset:

  • v110
  • v110_wp80
  • v110_xp
  • v120
  • v120_wp81
  • v140

In most desktop scenarios, v110_xp is what people want. It contains a statically linked C runtime lib. This is the one that gets included by bundle_e_sqlite3 for net45.

For UWP, v140 is the one you want.

In general, nobody cares about this. The bundles do the right thing. But the options are there for people who need fine-grained control over such things.

e_sqlite3 builds for Linux and Mac

SQLitePCLRaw.lib.e_sqlite3 packages are provided for Linux and Mac. Both bundle_green and bundle_e_sqlite3 have a dependency on these for net35/net40/net45, so that these bundles will "do the right thing" when used with Mono on Linux and Mac.

NetStandard

Release 1.0 supports netstandard. However, it also still includes some PCL profiles and platform-specific builds, some of which should be unnecessary. I may at some point simplify things by removing redundant stuff and letting netstandard be used everywhere it can be.

Windows Phone Silverlight

Two packages are provided for compatibility with Windows Phone 8.0 and Windows Phone 8.1 Silverlight:

  • SQLitePCLRaw.provider.e_sqlite3.wp80
  • SQLitePCLRaw.lib.e_sqlite3.v110_wp80

These environments do not support pinvoke, so it's a special case. The e_sqlite3 provider is the only one available.

Note that bundle_green and bundle_e_sqlite3 both support Windows Phone Silverlight.

CONTENT BELOW THIS LINE IS NOT FULLY UPDATED FOR 1.0

How do I build this?

For all practical purposes, it's impossible. :-)

gen_build.cs is a C# script which generates a solution with all the project configurations in the bld folder, along with other files for the build system.

On my build machine, I have Visual Studio 2012 and Visual Studio 2013 (update 2) and Visual Studio 2015 and Xamarin Android + iOS and
the relevant Android SDK(s).

build_mac.sh builds the iOS libraries and has to be run on the mac. The resulting assemblies are actually committed to the repository so the main build process can use them. Run apple/libs/mac/cp_mac.ps1 to copy the necessary files over to the bld directory.

Builds for sqlite and sqlcipher for Mac, iOS, and Android also happen on a Mac. See the sh files in the apple directory. For Android, run ndk-build in android/sqlite3.

Can this library be used to write a mobile app?

Technically, yes, but that's not what you want to do. This is not the sort of SQLite library you would use to write an app. It is a very thin C# wrapper around the C API for SQLite. It's "raw".

Consequently, as much as possible, this library follows the stylistic conventions of SQLite, not those of the .NET/C# world.

For example, the C function for opening a SQLite file is sqlite3_open(), so this API provides a method called sqlite3_open(), not Sqlite3Open().

Similarly, the functions in this API return integer error codes rather than throwing .NET exceptions, because that's how the SQLite C API works.

As a library for app developers, this library is downright hostile. It feels like using C. Intentionally.

So if this library is so unfriendly, why does it exist at all?

This library is designed to be the common portable layer upon which friendlier wrappers can be built. Right now, every C# SQLite library writes their own P/Invoke and COM and marshaling and stuff. Build on this library instead and focus more on the upper layer and its goal of providing a pleasant, easy-to-use API for app developers.

How does this compare to sqlite-net?

sqlite-net is a very popular SQLite wrapper by Frank Krueger (@praeclarum). Unlike SQLitePCL.raw, it is designed to make writing apps easier. It even includes a lightweight ORM, and some basic support for LINQ.

SQLitePCL.raw wants to replace the bottom half of sqlite-net so that it can become a PCL.

In fact, that has happened. Frank Krueger has released a NuGet package (sqlite-net-pcl) which is SQLite-net with SQLitePCL.raw underneath:

https://www.nuget.org/packages/sqlite-net-pcl/

When people ask me to recommend a friendlier SQLite wrapper, sqlite-net is the one that I usually recommend.

How does this compare to SQLitePCL.pretty?

SQLitePCL.pretty is another friendly SQLite API wrapper. It is built on top of SQLitePCL.raw, and its name resembles my SQLitePCL.Ugly wrapper (described below), but I am not the developer, and I'm afraid I have no actual experience using it. SQLitePCL.pretty is developed by @bordoley, who has also been a contributor of several fine pull requests to SQLitePCL.raw itself.

@bordoley's own description of SQLitePCL.pretty:

"It is designed to make interacting with the SQLite API easier, exposing the full feature set of SQLite in an idiomatic and pretty C# API.

Interesting features include the ability to iterate through query result sets using LINQ, support for binary streaming of data in and out of SQLite using .NET streams, and a powerful async API built on the RX framework."

How does this compare to System.Data.SQLite?

System.Data.SQLite is an ADO.NET-style SQLite wrapper developed by the core SQLite team. It is very full-featured, supporting LINQ and Entity Framework. And for obvious reasons, it does a fantastic job of the SQLite side of things. But it is not at all mobile-friendly.

How does this compare to Mono.Data.Sqlite?

Mono.Data.Sqlite is an ADO.NET-style SQLite wrapper which is built into Mono and the Xamarin platform. It shares a common ancestry with System.Data.SQLite, as both began as forks from the same code.

How does this compare to Microsoft.Data.Sqlite?

Microsoft.Data.Sqlite is an ADO.NET-style SQLite wrapper which is part of the ASP.NET 5 / EF7 effort at Microsoft.

How does this compare to SQLitePCL?

SQLitePCL is a SQLite Portable Class Library released on Codeplex by MS Open Tech.

This library is a fork of that code. Sort of.

It is a fork in the 2007 sense of the word. I made significant use of the code. I preserved copyright notices.

However, this is not the the sort of fork which is created for the purpose of producing a pull request. The changes I've made are so extensive that I do not plan to submit a pull request unless one is requested. I plan to maintain this code going forward.

So what is the architecture of this library?

Even within this thin library, there are three layers to be explained:

At the very bottom is the SQLite library itself. Written in C. This is unmanaged code, compiled for x86 or ARM or whatever.

Building on that, SQLitePCL.raw has three layers.

(1) We need something that can call the C code. For the Xamarin implementations this is DllImport (aka P/Invoke). For Windows Phone 8, this is a C++ wrapper. For the others, it is both. In either case, this presents an extremely low-level API. C pointers become System.IntPtr. Strings are not actually .NET strings, but rather, are in utf-8 encoding, represented in C# as either an IntPtr or a byte[].

(2) Next layer up, we have a C# layer which makes things just a tiny bit friendlier. Not much. It maps strings to/from utf8. And it manages delegates. The implementation of this layer varies depending on which assembly it is. For the PCL assembly itself (the Bait assembly), this is implemented as a set of stubs that throw errors.

(3) Finally, we have one more layer called "raw".
This layer is the top layer of the PCL, the one that is presented publicly. It is identical in all of the assemblies, portable or not. It adds one more C# nicety, which is that all IntPtrs are packaged up inside typed wrapper classes. For example, at the level of the C API, a database connection is represented by a sqlite3*. One layer up, inside the C# code, this becomes an IntPtr, and it remains an IntPtr at each layer until the top one (raw) which instead uses an instance of the sqlite3 class, which does nothing much except contain an IntPtr. In other words, it adds nothing except type checking.

For example, consider the C function sqlite3_prepare_v2(). In C, this function looks like this:

int sqlite3_prepare_v2(
  sqlite3* db,
  const char* pzSql,
  int nByte,
  sqlite3_stmt** ppStmt,
  const char** pzTail
  );

One layer up, it becomes:

[DllImport(SQLITE_DLL, CallingConvention = CallingConvention.Cdecl)]
public static extern int sqlite3_prepare_v2(
  IntPtr db, 
  byte[] pSql, 
  int nBytes, 
  out IntPtr stmt, 
  out IntPtr ptrRemain
  );

Both the sqlite3 and the sqlite3_stmt pointers became IntPtr, thus losing their type info and our ability to distinguish them by type. The string argument became a byte[], because it's utf8. The pzTail argument for returning a string becomes an IntPtr, but is also a utf8 C string.

One layer up, in the interface, the function looks like this:

int sqlite3_prepare_v2(
  IntPtr db, 
  string sql, 
  out IntPtr stmt, 
  out string remain
  );

The utf8 stuff is gone, and we've got strings. But IntPtr is still there.

Finally, in the raw API, this function is:

static public int sqlite3_prepare_v2(
  sqlite3 db, 
  string sql, 
  out sqlite3_stmt stmt, 
  out string tail
  );

The sqlite3 and sqlite3_stmt classes are those typed wrappers for IntPtrs that I mentioned. They have the exact same names as their counterparts in the SQLite C code.

Is there anything else in those IntPtr classes?

Actually, yes, glad you asked. Several of them support IDisposable as well. And there is also a little bit of plumbing to make sure that each pointer from the C layer lives inside only one instance of its corresponding IntPtr class.

So those IntPtr classes don't have any methods on them?

Nope.

What is SQLitePCL.Ugly?

Well, it's a bunch of extension methods for the IntPtr classes. It's like a fourth layer which provides method call syntax. It also switches the error handling model from integer return codes to exception throwing.

For example, the sqlite3_stmt class represents a statement handle, but you still have to do things like this:

int rc;

sqlite3 db;
rc = raw.sqlite3_open(":memory:", out db);
if (rc != raw.SQLITE_OK)
{
    error
}
sqlite3_stmt stmt;
rc = raw.sqlite3_prepare(db, "CREATE TABLE foo (x int)", out stmt);
if (rc != raw.SQLITE_OK)
{
    error
}
rc = raw.sqlite3_step(stmt);
if (rc == raw.SQLITE_DONE)
{
    whatever
}
else
{
    error
}
raw.sqlite3_finalize(stmt);

The Ugly layer allows me to do things like this:

using (sqlite3 db = ugly.open(":memory:"))
{
    sqlite3_stmt stmt = db.prepare("CREATE TABLE foo (x int)");
    stmt.step();
}

This exception-throwing wrapper exists so that I can have something easier against which to write tests. It retains all the "lower-case and underscores" ugliness of the layer(s) below.
It does not do things "The C# Way". As such, this is not a wrapper intended for public consumption.

But why did you have to make the Ugly layer, er, ugly?

I am very familiar with the underlying SQLite C API. I just wanted to write tests against something similar to it.

Wait a minute -- you're not a true camelCase believer, are you?

Guilty. I actually kinda like the old "lower-case and underscores" convention from my Unix days.

Also, sometimes when I am driving alone in my truck, I listen to country music.

Why do some tests fail on iOS and/or Android?

Because the version of SQLite preinstalled on the device or emulator is too old.

For example, the function sqlite3_close_v2() was added in SQLite version 3.7.14. As of Android KitKat, all versions of Android have shipped with SQLite 3.7.11 or older.

In practice, these issues are commonly handled by avoiding the use of new-ish SQLite functions. Alternatively, you can bundle a recent version of SQLite into your mobile app rather than using the build that is preinstalled on the platform. (See below for how to get SQLitePCL.raw to do this for you.)

Why are you making this so complicated?

Hey, don't blame me. I'm not making this complicated. I'm just trying to support all the valid use cases.

And more importantly, it is critical for the app to get this right. Here's why:

If you have two instances of the SQLite library linked into your app, you can corrupt a SQLite database file.

That's bad. And it's kind of an easy mistake to make, especially on mobile platforms where the OS provides SQLite preinstalled.

Whoa. I don't want my SQLite files corrupted. How do I make sure that won't happen?

On iOS/Android, you have two choices:

  1. Only use the SQLite provided by the OS. Make sure your that no part of your app bundles another copy of the SQLite library.

  2. Understand all the linkage issues and be very careful.

On other platforms, make sure you are including exactly one instance of the SQLite library.

On WinRT-ish platforms, why do I get "Unable to load DLL 'sqlite3': The specified module could not be found." ?

When using any of the RT flavored forms of Windows (Windows Store, Metro, WP81, etc) you must add a reference to the Visual C++ runtime extension SDK.