/// <summary>
/// 访问Lambda表达式所有运算符（从句、二元运算符）
/// </summary>
/// <param name="node">节点</param>
/// <returns></returns>
protected override Expression VisitBinary(BinaryExpression node)
{
// 遇到从句将两边条件合并
BooleanClause clause;
if (ClauseMapping.TryGetValue(node.NodeType, out clause))
{
var leftVisitor = new SimpleVisitor();
leftVisitor.Visit(node.Left);
var rightVisitor = new SimpleVisitor();
rightVisitor.Visit(node.Right);
_filter = new CombinedQueryFilter(leftVisitor._filter, rightVisitor._filter, clause);
return(node);
}
// 遇到二元运算符则将运算逻辑拆分为独立条件
BinaryOperation symbol;
if (OperationMapping.TryGetValue(node.NodeType, out symbol))
{
var leftVisitor = new SimpleVisitor();
leftVisitor.Visit(node.Left);
var rightVisitor = new SimpleVisitor();
rightVisitor.Visit(node.Right);
var x = new SingleQueryFilter();
x.AddPredicate(leftVisitor._fieldName, symbol, rightVisitor._value);
_filter = x;
return(node);
}
throw new NotSupportedException($"不支将 Lambda 表达式解析为 {nameof(QueryFilter)}，请确保右侧的表达式是一个符合规范的二元表达式。");
}
/// <summary>
/// 将Lambda表达式转换为条件对象
/// </summary>
/// <typeparam name="T">映射类型</typeparam>
/// <param name="expression">Lambda表达式</param>
/// <returns></returns>
public static QueryFilter Where <T>(Expression <Func <T, bool> > expression)
{
Guard.ArgumentNotNull(expression, nameof(expression));
var visitor = new SimpleVisitor();
visitor.Visit(expression);
return(visitor.Filter);
}
