public static Expression <Func <T, bool> > And <T>(this Expression <Func <T, bool> > exp1,
Expression <Func <T, bool> > exp2)
{
if (exp1 == null)
{
return(exp2);
}
if (exp2 == null)
{
return(exp1);
}
// 这种拼接方式在调用的时候会报 x not found。
// 因为 表达式1 和表达式2 的 x 为不同的对象，
// 而下面的拼接 使用的是表达式1的x.
// return Expression.Lambda<Func<T, bool>>(Expression.AndAlso(exp1.Body, exp2.Body), exp1.Parameters);
ParameterExpression newParameter = Expression.Parameter(typeof(T), "c");
NewExpressionVisitor visitor = new NewExpressionVisitor(newParameter);
var left = visitor.Replace(exp1.Body);
var right = visitor.Replace(exp2.Body);
var body = Expression.Add(left, right);
return(Expression.Lambda <Func <T, bool> >(body, newParameter));
}
/// <summary>
/// 非 !expr
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="expr"></param>
/// <returns></returns>
public static Expression <Func <T, bool> > Not <T>(this Expression <Func <T, bool> > expr)
{
ParameterExpression newParameter = Expression.Parameter(typeof(T), "c");
NewExpressionVisitor visitor = new NewExpressionVisitor(newParameter);
var temp = visitor.Visit(expr.Body);
var body = Expression.Not(temp);
return(Expression.Lambda <Func <T, bool> >(body, newParameter));
}
public static Expression <Func <T, bool> > Or <T>(this Expression <Func <T, bool> > expr1, Expression <Func <T, bool> > expr2)
{
ParameterExpression newParameter = Expression.Parameter(typeof(T), "c");
NewExpressionVisitor visitor = new NewExpressionVisitor(newParameter);
var left = visitor.Replace(expr1.Body);
var right = visitor.Replace(expr2.Body);
var body = Expression.Or(left, right);
return(Expression.Lambda <Func <T, bool> >(body, newParameter));
}
/// <summary>
/// 合并表达式(Or)
/// </summary>
/// <typeparam name="TEntity"></typeparam>
/// <param name="leftExpression"></param>
/// <param name="rightExpression"></param>
/// <returns></returns>
public static Expression <Func <TEntity, bool> > Or <TEntity>(this Expression <Func <TEntity, bool> > leftExpression, Expression <Func <TEntity, bool> > rightExpression)
{
ParameterExpression newParameter = Expression.Parameter(typeof(TEntity), "parameter");
NewExpressionVisitor visitor = new NewExpressionVisitor(newParameter);
var left = visitor.Replace(leftExpression.Body);
var right = visitor.Replace(rightExpression.Body);
var body = Expression.Or(left, right);
return(Expression.Lambda <Func <TEntity, bool> >(body, newParameter));
}
public static Expression <Func <T, bool> > Or <T>(this Expression <Func <T, bool> > exp1, Expression <Func <T, bool> > exp2)
{
if (exp1 == null)
{
return(exp2);
}
if (exp2 == null)
{
return(exp1);
}
ParameterExpression newPara = Expression.Parameter(typeof(T), "c");
NewExpressionVisitor visitor = new NewExpressionVisitor(newPara);
var left = visitor.Replace(exp1.Body);
var right = visitor.Replace(exp2.Body);
var body = Expression.Or(left, right);
return(Expression.Lambda <Func <T, bool> >(body, newPara));
}
