Support for Combine

CHANGELOG.md

@@ -56,14 +56,17 @@ GRDB adheres to [Semantic Versioning](https://semver.org/), with one expection:
 - [#539](https://github.com/groue/GRDB.swift/pull/539): Expose joining methods of both requests and associations
 - [#542](https://github.com/groue/GRDB.swift/pull/542): Move eager loading of hasMany associations to FetchRequest
 - [#546](https://github.com/groue/GRDB.swift/pull/546) by [@robcas3](https://github.com/robcas3): Fix SPM errors with Xcode 11 beta
-- You can now [combine](README.md#valueobservationcombine) up to eight ValueObservations in a single shot.
+- [#549](https://github.com/groue/GRDB.swift/pull/549) Support for Combine
 
 ### Documentation Diff
 
 The [Define Record Requests](Documentation/GoodPracticesForDesigningRecordTypes.md#define-record-requests) chapter of the The [Good Practices for Designing Record Types](Documentation/GoodPracticesForDesigningRecordTypes.md) has been rewritten. Yes, good practices evolve.
 
 The [Examples of Record Definitions](README.md#examples-of-record-definitions) has been extended with a sample record optimized for fetching performance.
 
+The [ValueObservation](README.md#valueobservation) chapter has been updated with the new APIs.
+
+
 ### API Diff
 
 ```diff

Documentation/AssociationsBasics.md

@@ -827,8 +827,8 @@ Those requests can also turn out useful when you want to track their changes wit
 ```swift
 // Track changes in the author's books:
 let author: Author = ...
-ValueObservation
-    .trackingAll(author.books)
+author.books
+    .observationForAll()
     .start(in: dbQueue) { (books: [Book]) in
         print("Author's book have changed")
     }

Documentation/GRDB3MigrationGuide.md

@@ -44,7 +44,7 @@ To guarantee asynchronous notifications, and never ever block your main thread,
 
 ```swift
 // On main queue
-var observation = ValueObservation.trackingAll(Player.all())
+var observation = Player.observationForAll()
 observation.scheduling = .async(onQueue: .main, startImmediately: true)
 let observer = try observation.start(in: dbQueue) { (players: [Player]) in
     // On main queue

GRDB.xcodeproj/project.pbxproj

@@ -610,9 +610,9 @@
 		56A8C2331D1914540096E9D4 /* UUID.swift in Sources */ = {isa = PBXBuildFile; fileRef = 56A8C22F1D1914540096E9D4 /* UUID.swift */; };
 		56A8C2471D1918F00096E9D4 /* FoundationNSUUIDTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 56A8C2361D1914790096E9D4 /* FoundationNSUUIDTests.swift */; };
 		56A8C2481D1918F00096E9D4 /* FoundationUUIDTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 56A8C21E1D1914110096E9D4 /* FoundationUUIDTests.swift */; };
-		56AACAA822ACED7100A40F2A /* Passthrough.swift in Sources */ = {isa = PBXBuildFile; fileRef = 56AACAA722ACED7100A40F2A /* Passthrough.swift */; };
-		56AACAA922ACED7100A40F2A /* Passthrough.swift in Sources */ = {isa = PBXBuildFile; fileRef = 56AACAA722ACED7100A40F2A /* Passthrough.swift */; };
-		56AACAAA22ACED7100A40F2A /* Passthrough.swift in Sources */ = {isa = PBXBuildFile; fileRef = 56AACAA722ACED7100A40F2A /* Passthrough.swift */; };
+		56AACAA822ACED7100A40F2A /* Fetch.swift in Sources */ = {isa = PBXBuildFile; fileRef = 56AACAA722ACED7100A40F2A /* Fetch.swift */; };
+		56AACAA922ACED7100A40F2A /* Fetch.swift in Sources */ = {isa = PBXBuildFile; fileRef = 56AACAA722ACED7100A40F2A /* Fetch.swift */; };
+		56AACAAA22ACED7100A40F2A /* Fetch.swift in Sources */ = {isa = PBXBuildFile; fileRef = 56AACAA722ACED7100A40F2A /* Fetch.swift */; };
 		56AE64122229A53700AD1B0B /* HasOneThroughAssociation.swift in Sources */ = {isa = PBXBuildFile; fileRef = 56AE64112229A53700AD1B0B /* HasOneThroughAssociation.swift */; };
 		56AE64132229A53700AD1B0B /* HasOneThroughAssociation.swift in Sources */ = {isa = PBXBuildFile; fileRef = 56AE64112229A53700AD1B0B /* HasOneThroughAssociation.swift */; };
 		56AE64142229A53700AD1B0B /* HasOneThroughAssociation.swift in Sources */ = {isa = PBXBuildFile; fileRef = 56AE64112229A53700AD1B0B /* HasOneThroughAssociation.swift */; };
@@ -1222,7 +1222,7 @@
 		56A8C21E1D1914110096E9D4 /* FoundationUUIDTests.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = FoundationUUIDTests.swift; sourceTree = "<group>"; };
 		56A8C22F1D1914540096E9D4 /* UUID.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = UUID.swift; sourceTree = "<group>"; };
 		56A8C2361D1914790096E9D4 /* FoundationNSUUIDTests.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = FoundationNSUUIDTests.swift; sourceTree = "<group>"; };
-		56AACAA722ACED7100A40F2A /* Passthrough.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = Passthrough.swift; sourceTree = "<group>"; };
+		56AACAA722ACED7100A40F2A /* Fetch.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = Fetch.swift; sourceTree = "<group>"; };
 		56AE64112229A53700AD1B0B /* HasOneThroughAssociation.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = HasOneThroughAssociation.swift; sourceTree = "<group>"; };
 		56AE6423222AAC9500AD1B0B /* AssociationHasOneThroughSQLTests.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = AssociationHasOneThroughSQLTests.swift; sourceTree = "<group>"; };
 		56AF746A1D41FB9C005E9FF3 /* DatabaseValueConvertibleEscapingTests.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = DatabaseValueConvertibleEscapingTests.swift; sourceTree = "<group>"; };
@@ -1999,8 +1999,8 @@
 			children = (
 				5613ED3E21A95A8B00DC7A68 /* Combine.swift */,
 				564CE4D521B2DEB500652B19 /* CompactMap.swift */,
+				56AACAA722ACED7100A40F2A /* Fetch.swift */,
 				5613ED3421A95A5C00DC7A68 /* Map.swift */,
-				56AACAA722ACED7100A40F2A /* Passthrough.swift */,
 				564CE59621B7A8B500652B19 /* RemoveDuplicates.swift */,
 				5613ED4321A95B2C00DC7A68 /* ValueReducer.swift */,
 			);
@@ -2720,7 +2720,7 @@
 				5695962B222C462D002CB7C9 /* HasManyThroughAssociation.swift in Sources */,
 				565490D31D5AE252005622CB /* (null) in Sources */,
 				566475D91D981D5E00FF74B8 /* SQLOperators.swift in Sources */,
-				56AACAAA22ACED7100A40F2A /* Passthrough.swift in Sources */,
+				56AACAAA22ACED7100A40F2A /* Fetch.swift in Sources */,
 				566B910F1FA4C3970012D5B0 /* Database+Statements.swift in Sources */,
 				56F5ABDD1D814330001F60CB /* UUID.swift in Sources */,
 				565490CB1D5AE252005622CB /* (null) in Sources */,
@@ -2780,7 +2780,7 @@
 				5613ED4921A95C1200DC7A68 /* ValueObservation+Row.swift in Sources */,
 				566B91361FA4D3810012D5B0 /* TransactionObserver.swift in Sources */,
 				564CE43221AA901800652B19 /* ValueObserver.swift in Sources */,
-				56AACAA922ACED7100A40F2A /* Passthrough.swift in Sources */,
+				56AACAA922ACED7100A40F2A /* Fetch.swift in Sources */,
 				5605F1721C672E4000235C62 /* DatabaseValueConvertible+RawRepresentable.swift in Sources */,
 				56CEB5141EAA324B00BFAF62 /* FTS3+QueryInterface.swift in Sources */,
 				566475CF1D981D5E00FF74B8 /* SQLFunctions.swift in Sources */,
@@ -3310,7 +3310,7 @@
 				56CEB4F11EAA2EFA00BFAF62 /* FetchableRecord.swift in Sources */,
 				56D91AA22205E03700770D8D /* SQLRelation.swift in Sources */,
 				56300B781C53F592005A543B /* QueryInterfaceRequest.swift in Sources */,
-				56AACAA822ACED7100A40F2A /* Passthrough.swift in Sources */,
+				56AACAA822ACED7100A40F2A /* Fetch.swift in Sources */,
 				5605F18D1C6B1A8700235C62 /* SQLCollatedExpression.swift in Sources */,
 				5613ED5421A95DD000DC7A68 /* ValueObservation+Count.swift in Sources */,
 				566B91331FA4D3810012D5B0 /* TransactionObserver.swift in Sources */,

GRDB/Core/DatabasePool.swift

@@ -34,6 +34,10 @@ public final class DatabasePool: DatabaseWriter {
         return writer.path
     }
 
+    public var configuration: Configuration {
+        return writer.configuration
+    }
+
     // MARK: - Initializer
 
     /// Opens the SQLite database at path *path*.
@@ -547,6 +551,14 @@ extension DatabasePool : DatabaseReader {
         return try writer.reentrantSync(block)
     }
 
+    /// Asynchronously executes an update block in a protected dispatch queue.
+    ///
+    /// Eventual concurrent reads may see changes performed in the block before
+    /// the block completes.
+    public func unsafeAsyncWrite(_ block: @escaping (Database) -> Void) {
+        writer.async(block)
+    }
+
     // MARK: - Functions
 
     /// Add or redefine an SQL function.

GRDB/Core/DatabaseQueue.swift

@@ -320,6 +320,10 @@ extension DatabaseQueue {
         return try writer.reentrantSync(block)
     }
 
+    public func unsafeAsyncWrite(_ block: @escaping (Database) -> Void) {
+        writer.async(block)
+    }
+
     // MARK: - Functions
 
     /// Add or redefine an SQL function.

GRDB/Core/DatabaseReader.swift

@@ -166,9 +166,9 @@ public protocol DatabaseReader : class {
     /// - returns: a TransactionObserver
     func add<Reducer: ValueReducer>(
         observation: ValueObservation<Reducer>,
-        onError: ((Error) -> Void)?,
+        onError: @escaping (Error) -> Void,
         onChange: @escaping (Reducer.Value) -> Void)
-        throws -> TransactionObserver
+        -> TransactionObserver
 
     /// Remove a transaction observer.
     func remove(transactionObserver: TransactionObserver)
@@ -257,11 +257,11 @@ public final class AnyDatabaseReader : DatabaseReader {
     /// :nodoc:
     public func add<Reducer: ValueReducer>(
         observation: ValueObservation<Reducer>,
-        onError: ((Error) -> Void)?,
+        onError: @escaping (Error) -> Void,
         onChange: @escaping (Reducer.Value) -> Void)
-        throws -> TransactionObserver
+        -> TransactionObserver
     {
-        return try base.add(observation: observation, onError: onError, onChange: onChange)
+        return base.add(observation: observation, onError: onError, onChange: onChange)
     }
 
     /// :nodoc:

GRDB/Core/DatabaseSnapshot.swift

@@ -100,36 +100,41 @@ extension DatabaseSnapshot {
 
     public func add<Reducer: ValueReducer>(
         observation: ValueObservation<Reducer>,
-        onError: ((Error) -> Void)?,
+        onError: @escaping (Error) -> Void,
         onChange: @escaping (Reducer.Value) -> Void)
-        throws -> TransactionObserver
+        -> TransactionObserver
     {
-        // Deal with initial value
-        switch observation.scheduling {
-        case .mainQueue:
-            if let value = try unsafeReentrantRead(observation.fetchFirst) {
-                if DispatchQueue.isMain {
-                    onChange(value)
-                } else {
-                    DispatchQueue.main.async {
+        // TODO: fetch asynchronously when possible
+        do {
+            // Deal with initial value
+            switch observation.scheduling {
+            case .mainQueue:
+                if let value = try unsafeReentrantRead(observation.fetchFirst) {
+                    if DispatchQueue.isMain {
                         onChange(value)
+                    } else {
+                        DispatchQueue.main.async {
+                            onChange(value)
+                        }
                     }
                 }
-            }
-        case let .async(onQueue: queue, startImmediately: startImmediately):
-            if startImmediately {
-                if let value = try unsafeReentrantRead(observation.fetchFirst) {
-                    queue.async {
-                        onChange(value)
+            case let .async(onQueue: queue, startImmediately: startImmediately):
+                if startImmediately {
+                    if let value = try unsafeReentrantRead(observation.fetchFirst) {
+                        queue.async {
+                            onChange(value)
+                        }
                     }
                 }
-            }
-        case let .unsafe(startImmediately: startImmediately):
-            if startImmediately {
-                if let value = try unsafeReentrantRead(observation.fetchFirst) {
-                    onChange(value)
+            case let .unsafe(startImmediately: startImmediately):
+                if startImmediately {
+                    if let value = try unsafeReentrantRead(observation.fetchFirst) {
+                        onChange(value)
+                    }
                 }
             }
+        } catch {
+            onError(error)
         }
 
         // Return a dummy observer, because snapshots never change