Adding REGEXP support.

Author: skent-mz

SQLite.Net.Tests/StringQueryTest.cs

@@ -63,5 +63,15 @@ public void StartsWith()
             List<Product> bs = db.Table<Product>().Where(x => x.Name.StartsWith("B")).ToList();
             Assert.AreEqual(1, bs.Count);
         }
+
+        [Test]
+        public void RegexTest()
+        {
+            var fs = db.Table<Product>().Where(x => x.Name.IsMatch("^F.*")).ToList();
+            Assert.AreEqual(2, fs.Count);
+            
+            var bs = db.Table<Product>().Where(x => x.Name.IsMatch(".*o$")).ToList();
+            Assert.AreEqual(1, bs.Count);
+        }
     }
 }

src/SQLite.Net/Interop/SQLiteApi.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Text.RegularExpressions;
 using SQLitePCL;
 
 namespace SQLite.Net2
@@ -14,6 +15,23 @@ public Result Open(string filename, out IDbHandle db, int flags, string zvfs)
             return (Result)r;
         }
 
+        public int BindRegexpFunction(IDbHandle db)
+        {
+            void RegexMatch(
+                sqlite3_context ctx,
+                object user_data,
+                sqlite3_value[] args)
+            {
+                var pattern = raw.sqlite3_value_text(args[0]).utf8_to_string();
+                var input = raw.sqlite3_value_text(args[1]).utf8_to_string();
+                var r = Regex.IsMatch(input, pattern);
+                raw.sqlite3_result_int(ctx, r ? 1 : 0);
+            }
+
+            var handle = (DbHandle)db;
+            return raw.sqlite3_create_function(handle.DbPtr, "REGEXP", 2, null, RegexMatch);
+        }
+
         public ExtendedResult ExtendedErrCode(IDbHandle db)
         {
             var internalDbHandle = (DbHandle)db;

src/SQLite.Net/SQLiteConnection.cs

@@ -145,6 +145,8 @@ public SQLiteConnection(string databasePath, SQLiteOpenFlags openFlags = SQLiteO
             if (r != Result.OK)
                 throw new SQLiteException(r, $"Could not open database file: {DatabasePath} ({r})");
 
+            sqlite.BindRegexpFunction(handle);
+
             Handle = handle ?? throw new NullReferenceException("Database handle is null");
             _open = true;
             databaseOpenFlags = openFlags;

src/SQLite.Net/TableQuery.cs

@@ -29,6 +29,7 @@
 using System.Reflection;
 using System.Runtime.CompilerServices;
 using System.Text;
+using System.Text.RegularExpressions;
 
 namespace SQLite.Net2
 {
@@ -541,6 +542,10 @@ private CompileResult CompileExpr( Expression expr, List<object> queryArgs)
                 {
                     sqlCall.AppendFormat("(replace({0}, {1}, {2}))", obj.CommandText, args[0].CommandText, args[1].CommandText);
                 }
+                else if (call.Method.Name == nameof(TableQueryExtensions.IsMatch) && args.Length == 2)
+                {
+                    sqlCall.AppendFormat("{0} REGEXP {1}", args[0].CommandText, args[1].CommandText);
+                }
                 else
                 {
                     sqlCall.Append(call.Method.Name.ToLower()).Append("(").Append(String.Join(",", args.Select(a => a.CommandText).ToArray())).Append(")");
@@ -830,4 +835,17 @@ private class CompileResult
             public object Value { get; set; }
         }
     }
+
+    public static class TableQueryExtensions
+    {
+        public static bool IsMatch(this ISerializable<string> a, string b)
+        {
+            return IsMatch(a.Serialize(), b);
+        }
+        
+        public static bool IsMatch(this string a, string b)
+        {
+            return Regex.IsMatch(a, b);
+        }
+    }
 }