Add MaxVarCharLength to all RDBMS string converters

Author: mythz

src/ServiceStack.OrmLite.MySql/Converters/MySqlStringConverters.cs

@@ -6,6 +6,9 @@ namespace ServiceStack.OrmLite.MySql.Converters
     public class MySqlStringConverter : StringConverter
     {
         public MySqlStringConverter() : base(255) {}
+        
+        //https://stackoverflow.com/a/37721151/85785
+        public override int MaxVarCharLength => UseUnicode ? 16383 : 21844;
 
         public override string MaxColumnDefinition => "LONGTEXT";
     }

src/ServiceStack.OrmLite.Oracle/Converters/OracleStringConverters.cs

@@ -14,6 +14,8 @@ protected OracleStringConverter(int stringLength) : base(stringLength)
 
         public override string MaxColumnDefinition => UseUnicode ? "NVARCHAR2(2000)" : "NVARCHAR2(4000)";
 
+        public override int MaxVarCharLength => UseUnicode ? 2000 : 4000;
+
         public override string GetColumnDefinition(int? stringLength)
         {
             if (stringLength.GetValueOrDefault() == StringLengthAttribute.MaxText)
@@ -36,6 +38,8 @@ public Oracle12StringConverter() : base(32767) {}
 
         public override string MaxColumnDefinition => UseUnicode ? "NVARCHAR2(16383)" : "NVARCHAR2(32767)";
 
+        public override int MaxVarCharLength => UseUnicode ? 16383 : 32767;
+
         public override string GetColumnDefinition(int? stringLength)
         {
             if (stringLength.GetValueOrDefault() == StringLengthAttribute.MaxText)

src/ServiceStack.OrmLite.PostgreSQL/Converters/PostgreSqlStringConverters.cs

@@ -9,6 +9,9 @@ public class PostgreSqlStringConverter : StringConverter
     {
         public override string ColumnDefinition => "TEXT";
 
+        //https://dba.stackexchange.com/questions/189876/size-limit-of-character-varying-postgresql
+        public override int MaxVarCharLength => UseUnicode ? 10485760 / 2 : 10485760;
+
         public override string GetColumnDefinition(int? stringLength)
         {
             //PostgreSQL doesn't support NVARCHAR when UseUnicode = true so just use TEXT

src/ServiceStack.OrmLite.SqlServer/Converters/SqlServerStringConverters.cs

@@ -9,6 +9,8 @@ namespace ServiceStack.OrmLite.SqlServer.Converters
     public class SqlServerStringConverter : StringConverter
     {
         public override string MaxColumnDefinition => UseUnicode ? "NVARCHAR(MAX)" : "VARCHAR(MAX)";
+        
+        public override int MaxVarCharLength => UseUnicode ? 4000 : 8000;
 
         public override string GetColumnDefinition(int? stringLength)
         {

src/ServiceStack.OrmLite.Sqlite/Converters/SqliteStringConverters.cs

@@ -5,5 +5,7 @@ namespace ServiceStack.OrmLite.Sqlite.Converters
     public class SqliteStringConverter : StringConverter
     {
         public override string MaxColumnDefinition => UseUnicode ? "NVARCHAR(1000000)" : "VARCHAR(1000000)";
+        
+        public override int MaxVarCharLength => 1000000;
     }
 }

src/ServiceStack.OrmLite/Converters/StringConverter.cs

@@ -17,6 +17,8 @@ public StringConverter(int stringLength)
 
         public int StringLength { get; set; }
 
+        public virtual int MaxVarCharLength => UseUnicode ? 8000 : 4000;
+
         protected string maxColumnDefinition;
         public virtual string MaxColumnDefinition
         {