Merge pull request stephencelis#1119 from GreenJell0/Statement_prepareRowIterator

Add prepareRowIterator method to an extension of Statement.

Author: nathanfallet

Documentation/Index.md

@@ -1963,6 +1963,14 @@ using the following functions.
         }
     }
     ```
+    Statements with results may be iterated over, using a `RowIterator` if
+    useful.
+    
+    ```swift
+    let emailColumn = Expression<String>("email")
+    let stmt = try db.prepare("SELECT id, email FROM users")
+    let emails = try! stmt.prepareRowIterator().map { $0[emailColumn] }
+    ```
 
   - `run` prepares a single `Statement` object from a SQL string, optionally
     binds values to it (using the statement’s `bind` function), executes,

Sources/SQLite/Core/Statement.swift

@@ -228,6 +228,21 @@ extension Statement: FailableIterator {
     }
 }
 
+extension Statement {
+    public func prepareRowIterator() -> RowIterator {
+        return RowIterator(statement: self, columnNames: self.columnNameMap)
+    }
+
+    var columnNameMap: [String: Int] {
+        var result = [String: Int]()
+        for (index, name) in self.columnNames.enumerated() {
+            result[name.quote()] = index
+        }
+
+        return result
+    }
+}
+
 extension Statement: CustomStringConvertible {
 
     public var description: String {

Tests/SQLiteTests/StatementTests.swift

@@ -23,4 +23,15 @@ class StatementTests: SQLiteTestCase {
         let blobValue = try! db.scalar(blobs.select(blobColumn).limit(1, offset: 0))
         XCTAssertEqual([], blobValue.bytes)
     }
+
+    func test_prepareRowIterator() {
+        let names = ["a", "b", "c"]
+        try! insertUsers(names)
+
+        let emailColumn = Expression<String>("email")
+        let statement = try! db.prepare("SELECT email FROM users")
+        let emails = try! statement.prepareRowIterator().map { $0[emailColumn] }
+
+        XCTAssertEqual(names.map({ "\($0)@example.com" }), emails.sorted())
+    }
 }