[英]How Build Lambda Expression Tree with multiple conditions
Note: I know it's much simple to create this using dynamic linq but I want to learn.注意:我知道使用动态 linq 创建它非常简单,但我想学习。
I want to create a lambda that "finds": Name=David AND Age=10.我想创建一个“发现”的 lambda:Name=David AND Age=10。
class Person
{
public int Age { get; set; }
public string Name { get; set; }
}
var lambda = LabmdaExpression<Person>("Name", "David", "Age", 10);
static Expression<Func<T, bool>> LabmdaExpression<T>(string property1, string value1, string property2, int value2)
{
ParameterExpression parameterExpression = Expression.Parameter(typeof(Person), "o");
MemberExpression memberExpression1 = Expression.PropertyOrField(parameterExpression, property1);
MemberExpression memberExpression2 = Expression.PropertyOrField(parameterExpression, property2);
ConstantExpression valueExpression1 = Expression.Constant(value1, typeof(string));
ConstantExpression valueExpression2 = Expression.Constant(value2, typeof(int));
BinaryExpression binaryExpression1 = Expression.Equal(memberExpression1, valueExpression1);
BinaryExpression binaryExpression2 = Expression.Equal(memberExpression2, valueExpression2);
var ret1 = Expression.Lambda<Func<T, bool>>(binaryExpression1, parameterExpression);
var ret2 = Expression.Lambda<Func<T, bool>>(binaryExpression2, parameterExpression);
}
Expression andExpression = Expression.AndAlso(binaryExpression1, binaryExpression2);
return Expression.Lambda<Func<T, bool>>(andExpression , parameterExpression);
Edit - comment编辑 - 评论
You just chain together all your expresions你只是把你所有的表达联系在一起
so in order to get this expression X AND (Y OR (Z OR Q))所以为了得到这个表达式 X AND (Y OR (Z OR Q))
Expression ZorQ = Expression.OrElse(zExp, qExp);
Expression YorZorQ = Expression.OrElse(yExp, ZorQ);
Expression XandYorZorQ = Expression.AndAlso(xExp, YorZorQ);
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