Pipeline

Pipeline is a powerful and performant Swift interface to SQLite featuring:

• Type-safe and type-agnostic database values.
• Thread-safe synchronous and asynchronous database access.
• Full support for transactions and savepoints.
• Custom SQL functions, including aggregate and window functions.
• Custom collating sequences.
• Custom commit, rollback, update, and busy handler hooks.
• Custom virtual tables.
• Custom FTS5 tokenizers.
• Optional support for pre-update hooks and sessions.
• Combine support.

Pipeline allows fast, easy database access with robust error handling. It is not a general-purpose object-relational mapper.

Installation

Swift Package Manager

Add a package dependency to https://github.com/sbooth/Pipeline in Xcode.

Manual or Custom Build

1. Clone the Pipeline repository.
2. swift build.

Quick Start

// Create a connection to an in-memory database
let connection = try Connection()

// Create a table
try connection.execute(sql: "CREATE TABLE t1(a,b);")

// Insert a row
try connection.execute(sql: "INSERT INTO t1(a,b) VALUES (?,?);", 
                       parameters: 33, "lulu")

// Retrieve the values
try connection.execute(sql: "SELECT a,b FROM t1;") { row in
    let a = try row.get(.int, at: 0)
    let b = try row.get(.string, at: 1)
}

Segue to Thread Safety

Pipeline uses SQLite with thread safety disabled for improved performance. While this increases performance, it also means a Connection object may only be accessed from a single thread or dispatch queue at a time.

Most applications should not create a Connection directly but instead should use a thread-safe ConnectionQueue.

// Create a queue serializing access to an in-memory database
let connectionQueue = try ConnectionQueue("myapp.database-connection-isolation-queue")

This creates a queue which may be used from multiple threads or dispatch queues safely. The queue serializes access to the database connection ensuring only a single operation occurs at a time. Database operations may be performed synchronously or asynchronously.

// Perform a synchronous database access
try connectionQueue.sync { connection in
    // Do something with `connection`
}

// Perform an asynchronous database access
connectionQueue.async { connection in
    // Do something with `connection`
} completion: { result in
    switch result {
        case .success:
            // 🎉
        case .failure(let error):
            // Handle any errors that occurred
    }
}

For databases using Write-Ahead Logging concurrent reading and writing is supported. Multiple read operations may be performed simultaneously using more than one ConnectionReadQueue instance. Write operations must always be confined to a single ConnectionQueue. A typical usage pattern is one global ConnectionQueue instance used for writing located in the application's delegate, with ConnectionReadQueue instances located in individual view or window controllers. When used with long-running read transactions each ConnectionReadQueue maintains a separate, consistent snapshot of the database that may be updated in response to database changes.

Design

The core of Pipeline is the types Connection, Statement, and Row.

• Connection is a connection to an SQLite database.

• Statement is a compiled SQL statement.

• Row is a single result row.

The fundamental type for a column value in a result row is DatabaseValue.

• DatabaseValue objects contain an integer, floating-point, textual, null, or BLOB value.

• DatabaseValue objects may be retrieved from result rows.

Type-safe column value access is provided by specializations of the ColumnValueConverter struct.

• ColumnValueConverter<T> converts a column value in a result row to an object of type T.

Type-safe SQL parameter binding is provided by SQLParameter objects.

• SQLParameter objects capture a value and bind it to an SQL parameter.

Thread-safe access to a database is provided by ConnectionQueue.

• ConnectionQueue serializes work items on a database connection.
• ConnectionReadQueue serializes read operations on a database connection.

Examples

Create a Connection to an In-Memory Database

let connection = try Connection()

This creates a connection for use on a single thread or dispatch queue only. Most applications should not create a Connection directly but instead should use a thread-safe ConnectionQueue.

Create a Table

try connection.execute(sql: "CREATE TABLE t1(a,b);")

The created table t1 has two columns, a and b.

Insert Data

for i in 0..<5 {
    try connection.execute(sql: "INSERT INTO t1(a,b) VALUES (?,?);",
                           parameters: .int(2*i), .int(2*i+1))
}

SQL parameters are passed as a sequence or series of values. Named parameters are also supported.

try connection.execute(sql: "INSERT INTO t1(a,b) VALUES (:a,:b);",
                       parameters: [":a": 100, ":b": 404])

Insert Data Efficiently

Rather than parsing SQL each time a statement is executed, it is more efficient to prepare a statement and reuse it.

let statement = try connection.prepare(sql: "INSERT INTO t1(a,b) VALUES (?,?);")
for i in 0..<5 {
    try statement.bind(.int(2*i), .int(2*i+1))
    try statement.execute()
    try statement.reset()
    try statement.clearBindings()
}

Fetch Data

The closure passed to execute() will be called with each result row.

try connection.execute(sql: "SELECT * FROM t1;") { row in
    let x = try row.get(.int, at: 0)
    let y = try row.optional(.int, at: 1)
}

row is a Row instance.

Perform a Transaction

try connection.transaction { connection, command in
    // Do something with `connection`
}

Transactions are committed by default after the transaction closure returns.

To roll back a transaction instead, set command to .rollback:

try connection.transaction { connection, command in
    // If a condition occurs that prevents the transaction from committing:
    command = .rollback
}

A rollback is not considered an error condition unless execution of the rollback fails.

Transactions may also return a value:

let (command, value) = try connection.transaction { connection, command -> Int64 in
    // ... some long and complex sequence of database commands inserting a row 
    return connection.lastInsertRowid
}

command contains the result of the transaction (whether it was committed or rolled back), and value is the value returned from the transaction closure.

Database transactions may also be performed asynchronously using ConnectionQueue.

connectionQueue.asyncTransaction { connection, command in
    // Do something with `connection`
} completion: { result in
    switch result {
        case .success:
            // 🎉
        case .failure(let error):
            // Handle any errors that occurred
    }
}

Custom SQL Functions

let rot13Mapping: [Character: Character] = [
    "A": "N", "B": "O", "C": "P", "D": "Q", "E": "R", "F": "S", "G": "T", "H": "U", "I": "V", "J": "W", "K": "X", "L": "Y", "M": "Z",
    "N": "A", "O": "B", "P": "C", "Q": "D", "R": "E", "S": "F", "T": "G", "U": "H", "V": "I", "W": "J", "X": "K", "Y": "L", "Z": "M",
    "a": "n", "b": "o", "c": "p", "d": "q", "e": "r", "f": "s", "g": "t", "h": "u", "i": "v", "j": "w", "k": "x", "l": "y", "m": "z",
    "n": "a", "o": "b", "p": "c", "q": "d", "r": "e", "s": "f", "t": "g", "u": "h", "v": "i", "w": "j", "x": "k", "y": "l", "z": "m"]

try connection.addFunction("rot13", arity: 1) { values in
    let value = values.first.unsafelyUnwrapped
    switch value {
        case .text(let t):
            return .text(String(t.map { rot13Mapping[$0] ?? $0 }))
        default:
            return value
    }
}

rot13 can now be used just like any other SQL function.

let statement = try connection.prepare(sql: "INSERT INTO t1(a) VALUES (rot13(?));")

Custom Collating Sequences

try connection.addCollation("localized_compare", { (lhs, rhs) -> ComparisonResult in
    lhs.localizedCompare(rhs)
})

localized_compare is now available as a collating sequence.

let statement = try connection.prepare(sql: "SELECT * FROM t1 ORDER BY a COLLATE localized_compare;")

Combine

Pipeline provides a Combine publisher for SQLite query results, allowing you to write elegant and powerful data processing code.

// CREATE TABLE event(description TEXT NOT NULL, date REAL NOT NULL);
struct Event {
    let description: String
    let date: Date
}

let eventConverter = RowConverter<Event> { row in
    let description = try row.text(at: 0)
    let date = try row.get(.dateWithTimeIntervalSinceReferenceDate, at: 1)
    return Event(description: description, date: date)
}

let connection = try Connection()

let sevenDaysAgo = Date() - 7 * 24 * 60 * 60

let publisher = connection.rowPublisher(sql: "SELECT description, date FROM event WHERE date >= ?1;") {
    try $0.bind(.timeIntervalSinceReferenceDate(sevenDaysAgo), toParameter: 1)
}

publisher
    .mapRows(eventConverter)

Miscellaneous

CSQLite

Pipeline uses CSQLite, a Swift package of the SQLite amalgamation with the carray, decimal, ieee754, series, sha3, and uuid extensions added, along with wrappers for C functions not easily usable from Swift.

SQLite Build Options

For performance reasons CSQLite is built without pre-update hook support. Unfortunately there is no way using Swift Package Manager to expose package features or build options, in this case the SQLite pre-update hook and the session extension. For this reason SQLite build options must be customized by changing to a local CSQLite package dependency and editing CSQLite/Package.swift.

License

Pipeline is released under the MIT License.