diff --git a/.github/workflows/swift.yml b/.github/workflows/swift.yml
new file mode 100644
index 0000000..46783f5
--- /dev/null
+++ b/.github/workflows/swift.yml
@@ -0,0 +1,39 @@
+name: Swift
+on: [push]
+jobs:
+
+  macos:
+    name: macOS
+    runs-on: macos-26
+    strategy:
+      fail-fast: false
+      matrix:
+        config: ["debug", "release"]
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v4
+    - name: Swift Version
+      run: swift --version
+    - name: Build
+      run: swift build -c ${{ matrix.config }}
+    - name: Test
+      run: swift test -c ${{ matrix.config }}
+
+  linux:
+    name: Linux (${{ matrix.container }})
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        container: ["swift:latest", "swiftlang/swift:nightly-noble"]
+        config: ["debug", "release"]
+    container: ${{ matrix.container }}
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v4
+    - name: Swift Version
+      run: swift --version
+    - name: Build
+      run: swift build -c ${{ matrix.config }}
+    - name: Test
+      run: swift test -c ${{ matrix.config }}
diff --git a/Sources/CoreModelSQLite/Database.swift b/Sources/CoreModelSQLite/Database.swift
index 379d7a4..76b4771 100644
--- a/Sources/CoreModelSQLite/Database.swift
+++ b/Sources/CoreModelSQLite/Database.swift
@@ -18,6 +18,19 @@ public actor SQLiteDatabase {
 
     internal let connection: SQLite.Connection
 
+    /// Fetched objects by entity and ID, mirroring CoreData's row cache: a repeated
+    /// `fetch(_:for:)` returns the cached value without touching SQLite, skipping both
+    /// the row query and the per-relationship queries that derive to-many values.
+    /// Predicate fetches also register their results, so ID lookups following a list
+    /// fetch are free.
+    ///
+    /// Writes drop the cached objects of every entity whose stored or derived values
+    /// they can change (see `invalidateCache(for:)`). The cache assumes this
+    /// actor is the database's only writer — the same coherency contract as separate
+    /// CoreData stacks on one store file. `SQLiteViewContext` reads its own connection
+    /// directly and always observes committed state.
+    internal var cache = [EntityName: [ObjectID: ModelData]]()
+
     /// Creates the schema eagerly, synchronously, as part of initialization — not lazily
     /// on first use. A `SQLiteViewContext` opens its own read-only connection to the same
     /// file and, being read-only, can never create the schema itself; without this, a
@@ -45,12 +58,24 @@ extension SQLiteDatabase: ModelStorage {
 
     public func fetch(_ entity: EntityName, for id: ObjectID) async throws -> ModelData? {
         try await asyncYield()
-        return try connection.fetch(entity, for: id, model: model)
+        if let cached = cache[entity]?[id] {
+            return cached
+        }
+        let value = try connection.fetch(entity, for: id, model: model)
+        if let value {
+            cache[entity, default: [:]][id] = value
+        }
+        return value
     }
 
     public func fetch(_ fetchRequest: FetchRequest) async throws -> [ModelData] {
         try await asyncYield()
-        return try connection.fetch(fetchRequest, model: model)
+        let values = try connection.fetch(fetchRequest, model: model)
+        // register results so subsequent ID lookups are cache hits
+        for value in values {
+            cache[fetchRequest.entity, default: [:]][value.id] = value
+        }
+        return values
     }
 
     public func fetchID(_ fetchRequest: FetchRequest) async throws -> [ObjectID] {
@@ -66,21 +91,25 @@ extension SQLiteDatabase: ModelStorage {
     public func insert(_ value: ModelData) async throws {
         try await asyncYield()
         try connection.insert(value, model: model)
+        invalidateCache(for: [value.entity])
     }
 
     public func insert(_ values: [ModelData]) async throws {
         try await asyncYield()
         try connection.insert(values, model: model)
+        invalidateCache(for: Set(values.lazy.map { $0.entity }))
     }
 
     public func delete(_ entity: EntityName, for id: ObjectID) async throws {
         try await asyncYield()
         try connection.delete(entity, for: id, model: model)
+        invalidateCache(for: [entity])
     }
 
     public func delete(_ entity: EntityName, for ids: [ObjectID]) async throws {
         try await asyncYield()
         try connection.delete(entity, for: ids, model: model)
+        invalidateCache(for: [entity])
     }
 }
 
@@ -90,6 +119,28 @@ internal extension SQLiteDatabase {
         await Task.yield()
         try Task.checkCancellation()
     }
+
+    /// Drop cached objects of every entity a write to the given entities can affect.
+    ///
+    /// A write to entity E touches E's own table, the foreign key columns of E's
+    /// relationship destinations, and their shared join tables. Derived to-many values
+    /// are computed only from those same foreign keys and join tables, so the affected
+    /// set is exactly E plus E's destination entities — including E-typed rows other
+    /// than the one written (e.g. reassigning a person to a new team also changes the
+    /// old team's `members`), which is why whole entity caches are dropped rather than
+    /// single objects.
+    func invalidateCache(for entities: Set<EntityName>) {
+        var affected = entities
+        for entity in entities {
+            guard let description = model.entities.first(where: { $0.id == entity }) else { continue }
+            for relationship in description.relationships {
+                affected.insert(relationship.destinationEntity)
+            }
+        }
+        for entity in affected {
+            cache[entity] = nil
+        }
+    }
 }
 
 internal extension Connection {
diff --git a/Tests/CoreModelSQLiteTests/CacheTests.swift b/Tests/CoreModelSQLiteTests/CacheTests.swift
new file mode 100644
index 0000000..8cd7d4c
--- /dev/null
+++ b/Tests/CoreModelSQLiteTests/CacheTests.swift
@@ -0,0 +1,143 @@
+import Foundation
+import Testing
+import CoreModel
+import SQLite
+@testable import CoreModelSQLite
+
+/// Verifies `SQLiteDatabase`'s object cache: repeated ID lookups are served from memory,
+/// and every write shape that can change a fetched representation — direct updates,
+/// inverse relationship changes, reassignment side effects, and deletes — invalidates
+/// the affected entries so reads never observe stale data.
+@Suite("Object Cache")
+struct CacheTests {
+
+    @Test func fetchByIDPopulatesCache() async throws {
+        let database = try makeDatabase()
+        let person = ModelData(
+            entity: "Person",
+            id: "person1",
+            attributes: ["name": .string("Alice"), "age": .int32(30)]
+        )
+        try await database.insert(person)
+        #expect(await database.cache["Person"]?["person1"] == nil)
+        let fetched = try #require(try await database.fetch("Person", for: "person1"))
+        #expect(await database.cache["Person"]?["person1"] == fetched)
+        // a second fetch returns the cached value
+        let cached = try #require(try await database.fetch("Person", for: "person1"))
+        #expect(cached == fetched)
+    }
+
+    @Test func fetchRequestRegistersResults() async throws {
+        let database = try makeDatabase()
+        let people = (0..<5).map { index in
+            ModelData(
+                entity: "Person",
+                id: ObjectID(rawValue: "person\(index)"),
+                attributes: ["name": .string("Person \(index)"), "age": .int32(Int32(20 + index))]
+            )
+        }
+        try await database.insert(people)
+        let results = try await database.fetch(FetchRequest(entity: "Person"))
+        #expect(results.count == 5)
+        let cache = await database.cache["Person"]
+        #expect(cache?.count == 5)
+        for value in results {
+            #expect(cache?[value.id] == value)
+        }
+    }
+
+    @Test func updateInvalidatesCachedObject() async throws {
+        let database = try makeDatabase()
+        var person = ModelData(
+            entity: "Person",
+            id: "person1",
+            attributes: ["name": .string("Alice"), "age": .int32(30)]
+        )
+        try await database.insert(person)
+        _ = try await database.fetch("Person", for: "person1")
+        // update through the same database
+        person.attributes["age"] = .int32(31)
+        try await database.insert(person)
+        #expect(await database.cache["Person"] == nil)
+        let fetched = try #require(try await database.fetch("Person", for: "person1"))
+        #expect(fetched.attributes["age"] == .int32(31))
+    }
+
+    @Test func writeInvalidatesInverseRelationship() async throws {
+        let database = try makeDatabase()
+        let team = ModelData(entity: "Team", id: "team1", attributes: ["name": .string("Red")])
+        try await database.insert(team)
+        // cache the team with no members
+        let cached = try #require(try await database.fetch("Team", for: "team1"))
+        #expect(cached.relationships["members"] == .toMany([]))
+        // inserting a person pointing at the team changes the team's derived `members`
+        let person = ModelData(
+            entity: "Person",
+            id: "person1",
+            attributes: ["name": .string("Alice")],
+            relationships: ["team": .toOne("team1")]
+        )
+        try await database.insert(person)
+        let fetched = try #require(try await database.fetch("Team", for: "team1"))
+        #expect(fetched.relationships["members"] == .toMany(["person1"]))
+    }
+
+    @Test func reassignmentInvalidatesOtherRows() async throws {
+        let database = try makeDatabase()
+        let teams = ["team1", "team2"].map {
+            ModelData(entity: "Team", id: ObjectID(rawValue: $0), attributes: ["name": .string($0)])
+        }
+        try await database.insert(teams)
+        let person = ModelData(
+            entity: "Person",
+            id: "person1",
+            attributes: ["name": .string("Alice")],
+            relationships: ["team": .toOne("team2")]
+        )
+        try await database.insert(person)
+        // cache team2 with its member
+        let cached = try #require(try await database.fetch("Team", for: "team2"))
+        #expect(cached.relationships["members"] == .toMany(["person1"]))
+        // claiming the person for team1 also changes team2's derived `members`,
+        // a row of the written entity other than the one written
+        var team1 = teams[0]
+        team1.relationships["members"] = .toMany(["person1"])
+        try await database.insert(team1)
+        let fetched = try #require(try await database.fetch("Team", for: "team2"))
+        #expect(fetched.relationships["members"] == .toMany([]))
+    }
+
+    @Test func deleteRemovesFromCache() async throws {
+        let database = try makeDatabase()
+        let person = ModelData(
+            entity: "Person",
+            id: "person1",
+            attributes: ["name": .string("Alice")]
+        )
+        try await database.insert(person)
+        _ = try await database.fetch("Person", for: "person1")
+        try await database.delete("Person", for: "person1")
+        #expect(await database.cache["Person"] == nil)
+        #expect(try await database.fetch("Person", for: "person1") == nil)
+    }
+
+    @Test func deleteNullifiesCachedReferences() async throws {
+        let database = try makeDatabase()
+        let team = ModelData(entity: "Team", id: "team1", attributes: ["name": .string("Red")])
+        let person = ModelData(
+            entity: "Person",
+            id: "person1",
+            attributes: ["name": .string("Alice")],
+            relationships: ["team": .toOne("team1")]
+        )
+        try await database.insert(team)
+        try await database.insert(person)
+        // cache the person with its team reference
+        let cached = try #require(try await database.fetch("Person", for: "person1"))
+        #expect(cached.relationships["team"] == .toOne("team1"))
+        // deleting the team nullifies the cached person's foreign key
+        try await database.delete("Team", for: "team1")
+        let fetched = try #require(try await database.fetch("Person", for: "person1"))
+        #expect(fetched.relationships["team"] == .null)
+    }
+}
diff --git a/Tests/CoreModelSQLiteTests/ProfessionalDriver/Model/VIN.swift b/Tests/CoreModelSQLiteTests/ProfessionalDriver/Model/VIN.swift
index dc076f7..bce2fa3 100644
--- a/Tests/CoreModelSQLiteTests/ProfessionalDriver/Model/VIN.swift
+++ b/Tests/CoreModelSQLiteTests/ProfessionalDriver/Model/VIN.swift
@@ -25,14 +25,20 @@ internal extension VehicleIdentificationNumber {
 
     static func isValid(_ vin: inout String) -> Bool {
         vin = vin.uppercased()
+        #if canImport(Darwin)
         if #available(iOS 16.0, *) {
             return vin.wholeMatch(of: /^[A-HJ-NPR-Z0-9]{17}$/) != nil
         } else {
             return Self.predicate.evaluate(with: vin)
         }
+        #else
+        return vin.wholeMatch(of: /^[A-HJ-NPR-Z0-9]{17}$/) != nil
+        #endif
     }
 
+    #if canImport(Darwin)
     nonisolated(unsafe) static let predicate = NSPredicate(format: "SELF MATCHES %@", "^[A-HJ-NPR-Z0-9]{17}$")
+    #endif
 }
 
 // MARK: - CustomStringConvertible