NHibernate:HqlGenerator:通过连接其他属性来创建计算属性

我正在尝试添加HqlGenerator，以允许NHibernate查询以下域实体上的计算属性：

public class User 
{
    public string FirstName { get; set; }
    public string LastName {get; set; }
    public string FullName
    {
        get { return FirstName + " " + LastName; }
    }
}

我创建了一个HQL生成器，如下所示：

public class UserFullName : BaseHqlGeneratorForProperty
{
    public UserFullName()
    {
        var properties = new List<MemberInfo> { typeof(User).GetProperty("FullName") };
        SupportedProperties = properties;
    }

    public override HqlTreeNode BuildHql(MemberInfo member, Expression expression, HqlTreeBuilder treeBuilder, IHqlExpressionVisitor visitor)
    {
        var user = visitor.Visit(expression).AsExpression();
        return treeBuilder.Concat(
            treeBuilder.Dot(user, treeBuilder.Ident("FirstName")),
            treeBuilder.Constant(" "),
            treeBuilder.Dot(user, treeBuilder.Ident("LastName"))
        );
    }
}

但是，稍后在NHibernate内部会引发异常：

NHibernate.Hql.Ast.ANTLR.QuerySyntaxException : Exception of type 'Antlr.Runtime.NoViableAltException' was thrown. [.FirstOrDefault[User](NHibernate.Linq.NhQueryable`1[User], Quote((x, ) => (String.op_Equality(x.FullName, Aaron Janes))), )]

有人能发现我做错了什么吗？

在BuildHQL（）中，您多次包含子表达式“user”。这是不可能的。你需要使用

var user1 = visitor.Visit(expression).AsExpression();
var user2 = visitor.Visit(expression).AsExpression();

并在Concat表达式中使用其中的每一项

var user1 = visitor.Visit(expression).AsExpression();
var user2 = visitor.Visit(expression).AsExpression();