我正在使用表达式构建一个围绕Web服务调用的API,以允许开发人员指定查询,并使ExpressionVisitor将表达式转换为查询字符串。请求是XML格式,其中特定元素包含查询字符串。
例如,我可以执行以下操作,这将检索所有银行名称为Bank 1或Bank 2的支票账户:
"bankname = 'Bank 1' or bankname = 'Bank 2'"
Web服务可以处理更复杂的查询,但现在我只需要用这个。所以我有一个CheckingAccount类:
我知道如何处理简单的本地变量(即string bankName = "Bank 2"),但处理其他类型的变量(例如var account = new CheckingAccount { BankName = "Bank 1" })要复杂得多。
最终,这些是我现在需要解决的重大问题。我知道还有更复杂的情况,但我目前并不太关心它们。
以下是我的表达式访问器(请注意CreateFilter方法上的泛型约束):
例如,我可以执行以下操作,这将检索所有银行名称为Bank 1或Bank 2的支票账户:
"bankname = 'Bank 1' or bankname = 'Bank 2'"
Web服务可以处理更复杂的查询,但现在我只需要用这个。所以我有一个CheckingAccount类:
[IntacctObject("checkingaccount")]
public class CheckingAccount : Entity
{
[IntacctElement("bankaccountid")]
public string Id { get; set; }
[IntacctElement("bankname")]
public string BankName { get; set; }
}
一个ExpressionVisitor的主要功能是将这样的表达式转换为查询:
Expression> expression = ca => ca.BankName == "Bank 1" || ca.BankName == "Bank 2"
“bankname ='Bank 1'或bankname ='Bank 2'”
这并不难。当我引入本地变量时,问题开始变得复杂起来:
var account = new CheckingAccount { BankName = "Bank 1" };
string bankName = "Bank 2";
Expression> expression = ca => ca.BankName == account.BankName || ca.BankName == bankName;
我知道如何处理简单的本地变量(即string bankName = "Bank 2"),但处理其他类型的变量(例如var account = new CheckingAccount { BankName = "Bank 1" })要复杂得多。
最终,这些是我现在需要解决的重大问题。我知道还有更复杂的情况,但我目前并不太关心它们。
以下是我的表达式访问器(请注意CreateFilter方法上的泛型约束):
internal class IntacctWebService30ExpressionVisitor : ExpressionVisitor
{
private readonly List _Filters = new List();
private IntacctWebServicev30SimpleQueryFilter _CurrentSimpleFilter;
private IntacctWebServicev30ComplexQueryFilter _CurrentComplexFilter;
private MemberExpression _CurrentMemberExpression;
public string CreateFilter(Expression> expression) where TEntity : Entity
{
Visit(expression);
string filter = string.Join(string.Empty, _Filters.Select(f => f.ToString()).ToArray());
return filter;
}
protected override Expression VisitBinary(BinaryExpression node)
{
switch (node.NodeType)
{
case ExpressionType.AndAlso:
case ExpressionType.OrElse:
_CurrentComplexFilter = new IntacctWebServicev30ComplexQueryFilter { ExpressionType = node.NodeType };
break;
case ExpressionType.Equal:
case ExpressionType.GreaterThan:
case ExpressionType.GreaterThanOrEqual:
case ExpressionType.LessThan:
case ExpressionType.LessThanOrEqual:
case ExpressionType.NotEqual:
_CurrentSimpleFilter = new IntacctWebServicev30SimpleQueryFilter { ExpressionType = node.NodeType };
break;
}
return base.VisitBinary(node);
}
protected override Expression VisitMember(MemberExpression node)
{
var attr = node.Member.GetAttribute();
if (attr != null)
_CurrentSimpleFilter.FieldName = attr.FieldName;
else
_CurrentMemberExpression = node;
return base.VisitMember(node);
}
protected override Expression VisitConstant(ConstantExpression node)
{
object value = Expression.Lambda>(node).Compile().Invoke();
string fieldValue = extraxtFieldValue(value, node);
_CurrentSimpleFilter.FieldValue = fieldValue;
if (_CurrentComplexFilter != null)
{
if (_CurrentComplexFilter.Left == null)
{
_CurrentComplexFilter.Left = _CurrentSimpleFilter;
}
else if (_CurrentComplexFilter.Right == null)
{
_CurrentComplexFilter.Right = _CurrentSimpleFilter;
_Filters.Add(_CurrentComplexFilter);
}
else
throw new InvalidOperationException();
}
else
{
_Filters.Add(_CurrentSimpleFilter);
}
return base.VisitConstant(node);
}
private string extraxtFieldValue(object value)
{
string fieldValue;
if (value is DateTime)
fieldValue = ((DateTime)value).ToString("yyyy-MM-dd");
else if (value is string)
fieldValue = value.ToString();
else if (value.GetType().IsEnum)
{
throw new NotImplementedException();
}
else
{
// Not sure if this is the best way to do this or not but can't figure out how
// else to get a variable value.
// If we are here then we are dealing with a property, field, or variable.
// This means we must extract the value from the object.
// In order to do this we will rely on _CurrentMemberExpression
if (_CurrentMemberExpression.Member.MemberType == MemberTypes.Property)
{
fieldValue = value.GetType().GetProperty(_CurrentMemberExpression.Member.Name).GetValue(value, null).ToString();
}
else if (_CurrentMemberExpression.Member.MemberType == MemberTypes.Field)
{
fieldValue = value.GetType().GetFields().First().GetValue(value).ToString();
}
else
{
throw new InvalidOperationException();
}
}
return fieldValue;
}
}
如果您需要更多细节,请告诉我...
谢谢