c# – 从Expression>生成动态UPDATE命令

我正在尝试基于表达式树生成UPDATE命令(用于批量更新).

假设以下UPDATE命令：

UPDATE Product
SET ProductTypeId = 123,ProcessAttempts = ProcessAttempts + 1

对于这样的表达式：

Expression<Func<Product,Product>> updateExpression = entity =>
    new Product() {
        ProductTypeId = 123,ProcessAttempts = entity.ProcessAttempts + 1
    };

如何生成命令的SET部分？

SET ProductTypeId = 123,ProcessAttempts = ProcessAttempts + 1

解决方法

这是一种非常简单的方法,但我希望它足够好：

private static string ConvertToSetCommand<T>(Expression<Func<T,T>> exp)
{
    if (exp.Body.NodeType != ExpressionType.MemberInit)
    {
        throw new ArgumentException("The expression must have an object initializer.","exp");
    }

    var builder = new StringBuilder("SET ",100);
    exp = (Expression<Func<T,T>>) new OmitParametersVisitor().Visit(exp);

    var memberInit = (MemberInitExpression) exp.Body;
    foreach (var assignment in memberInit.Bindings)
    {
        builder.Append(assignment.ToString());
        builder.Append(",");
    }
    builder.Length -= 2; // Remove the last comma

    return builder.ToString();
}

private class OmitParametersVisitor : ExpressionVisitor
{
    protected override Expression VisitMember(MemberExpression node)
    {
        if (node.Expression != null && node.Expression.NodeType == ExpressionType.Parameter)
        {
            return Expression.Parameter(node.Type,node.Member.Name);
        }
        else
        {
            return base.VisitMember(node);
        }
    }
}