C遍历表达式树以提取表名

public static class TableFinder
{
    public static IEnumerable<string> GetTableNames(this DataContext context, IQueryable queryable) {
        var visitor = new TableFindingVisitor(context.Mapping);
        visitor.Visit(queryable.Expression);
        return visitor.Tables.Select(t => t.TableName).Distinct().AsEnumerable();
    }

    class TableFindingVisitor : ExpressionVisitor
    {
        private readonly HashSet<MetaTable> foundTables = new HashSet<MetaTable>();
        private readonly MetaModel mapping;

        public TableFindingVisitor(MetaModel mapping) {
            this.mapping = mapping;
        }

        public override Expression Visit(Expression node) {
            return base.Visit(node);
        }

        protected override Expression VisitConstant(ConstantExpression node) {
            if (node.Type.GetGenericTypeDefinition() == typeof(Table<>))
                CheckType(node.Type.GetGenericArguments()[0]);
            return base.VisitConstant(node);
        }

        protected override Expression VisitMember(MemberExpression node) {
            CheckType(node.Member.DeclaringType);
            return base.VisitMember(node);
        }

        public IEnumerable<MetaTable> Tables { get { return foundTables; } }

        private void CheckType(Type t) {
            var table = mapping.GetTable(t);
            if (table != null && !foundTables.Contains(table))
                foundTables.Add(table);
        }
    }