Obtain the value of the lambda expression.

With the prevalence of LINQ, more and more expressions are used for LINQ and lmabda. as proposed in Net Framework 3.5, lambda expressions are an anonymous method, which is usually used to create delegation in LINQ. However, when we use lmabda expressions to implement some operations, it is very important to break down the internal expression tree structure. For example, we need to directly use t => T in some method calls. the name method gets the attribute name, so that we don't have to write the string ourselves, and the compiler can help us refactor and detect the attribute when it changes.

When we want to implement the above method, we will not only use anonymous delegation, but also use expression, which is located in system. LINQ. in the expressions namespace, you can find the specific information in msdn, which is not listed here. {Class. the format of attribute} is a memberexpression object, and the node type is memberaccess. Because the types of the attributes to be obtained are not necessarily the same, therefore, the Delegate for retrieving attribute names can only be defined as func <t, Object>. The Code is as follows:

public static string ResloveName<T>(Expression<Func<T, object>> expression)
{
    var exp = expression.Body as MemberExpression;
    string expStr = exp.ToString();
    return expStr.Substring(expStr.IndexOf(".") + 1);
}

The following code is available:

User user = new User { Name = "Xiao Ming" };
Expression<Func<User, bool>> exp = u => u.Name == user.Name;

If we want to use this Binary Expression to construct an SQL statement, how should we break down this expression? My approach is to first convert the subject of the expression to binaryexpression, then, determine whether the expressions in the left and right attributes are the same as the exp parameter expressions, and calculate the values of different expressions, used as a parameter. The Code is as follows:

BinaryExpression binaryExp = exp.Body as BinaryExpression;
Expression constantExp = (binaryExp.Left as MemberExpression).Expression == exp.Parameters[0] ? binaryExp.Right : binaryExp.Left;
string value = Expression.Lambda(constantExp).Compile().DynamicInvoke().ToString();

From the inheritance system, we can find that all generic expressions are inherited from lambdaexpression. Therefore, we can reload a method with the following code:

public static string ResloveName(Expression<Func<T, object>> expression)
{
    return ResloveName(expression as LambdaExpression);
}

public static string ResloveName(LambdaExpression expression)
{
    var exp = expression.Body as MemberExpression;
    string expStr = exp.ToString();
    return expStr.Substring(expStr.IndexOf(".") + 1);
}

I hope the above Code can help you in the application of expressions. Thank you!

Transferred from:Ahl5esoft.

Obtain the value of the lambda expression.