C#动态创建lambda表达式

/// <summary>
/// 创建lambda表达式：p=>true
/// </summary>
/// <typeparam name="T"></typeparam>
/// <returns></returns>
public static Expression<Func<T, bool>> True<T>()
{
return p => true;
}

/// <summary>
/// 创建lambda表达式：p=>false
/// </summary>
/// <typeparam name="T"></typeparam>
/// <returns></returns>
public static Expression<Func<T, bool>> False<T>()
{
return p => false;
}

/// <summary>
/// 创建lambda表达式：p=>p.propertyName
/// </summary>
/// <typeparam name="T"></typeparam>
/// <typeparam name="TKey"></typeparam>
/// <param name="sort"></param>
/// <returns></returns>
public static Expression<Func<T, TKey>> GetOrderExpression<T, TKey>(string propertyName)
{
ParameterExpression parameter = Expression.Parameter(typeof(T), "p");
return Expression.Lambda<Func<T, TKey>>(Expression.Property(parameter, propertyName), parameter);
}

/// <summary>
/// 创建lambda表达式：p=>p.propertyName == propertyValue
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="column"></param>
/// <param name="value"></param>
/// <returns></returns>
public static Expression<Func<T, bool>> CreateEqual<T>(string propertyName, string propertyValue)
{
ParameterExpression parameter = Expression.Parameter(typeof(T), "p");//创建参数p
MemberExpression member = Expression.PropertyOrField(parameter, propertyName);
ConstantExpression constant = Expression.Constant(propertyValue);//创建常数
return Expression.Lambda<Func<T, bool>>(Expression.Equal(member, constant), parameter);
}

/// <summary>
/// 创建lambda表达式：p=>p.propertyName != propertyValue
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="propertyName"></param>
/// <param name="propertyValue"></param>
/// <returns></returns>
public static Expression<Func<T, bool>> CreateNotEqual<T>(string propertyName, string propertyValue)
{
ParameterExpression parameter = Expression.Parameter(typeof(T), "p");//创建参数p
MemberExpression member = Expression.PropertyOrField(parameter, propertyName);
ConstantExpression constant = Expression.Constant(propertyValue);//创建常数
return Expression.Lambda<Func<T, bool>>(Expression.NotEqual(member, constant), parameter);
}

/// <summary>
/// 创建lambda表达式：p=>p.propertyName > propertyValue
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="column"></param>
/// <param name="value"></param>
/// <returns></returns>
public static Expression<Func<T, bool>> CreateGreaterThan<T>(string propertyName, string propertyValue)
{
ParameterExpression parameter = Expression.Parameter(typeof(T), "p");//创建参数p
MemberExpression member = Expression.PropertyOrField(parameter, propertyName);
ConstantExpression constant = Expression.Constant(propertyValue);//创建常数
return Expression.Lambda<Func<T, bool>>(Expression.GreaterThan(member, constant), parameter);
}

/// <summary>
/// 创建lambda表达式：p=>p.propertyName < propertyValue
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="column"></param>
/// <param name="value"></param>
/// <returns></returns>
public static Expression<Func<T, bool>> CreateLessThan<T>(string propertyName, string propertyValue)
{
ParameterExpression parameter = Expression.Parameter(typeof(T), "p");//创建参数p
MemberExpression member = Expression.PropertyOrField(parameter, propertyName);
ConstantExpression constant = Expression.Constant(propertyValue);//创建常数
return Expression.Lambda<Func<T, bool>>(Expression.LessThan(member, constant), parameter);
}

/// <summary>
/// 创建lambda表达式：p=>p.propertyName >= propertyValue
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="column"></param>
/// <param name="value"></param>
/// <returns></returns>
public static Expression<Func<T, bool>> CreateGreaterThanOrEqual<T>(string propertyName, string propertyValue)
{
ParameterExpression parameter = Expression.Parameter(typeof(T), "p");//创建参数p
MemberExpression member = Expression.PropertyOrField(parameter, propertyName);
ConstantExpression constant = Expression.Constant(propertyValue);//创建常数
return Expression.Lambda<Func<T, bool>>(Expression.GreaterThanOrEqual(member, constant), parameter);
}

/// <summary>
/// 创建lambda表达式：p=>p.propertyName <= propertyValue
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="column"></param>
/// <param name="value"></param>
/// <returns></returns>
public static Expression<Func<T, bool>> CreateLessThanOrEqual<T>(string propertyName, string propertyValue)
{
ParameterExpression parameter = Expression.Parameter(typeof(T), "p");//创建参数p
MemberExpression member = Expression.PropertyOrField(parameter, propertyName);
ConstantExpression constant = Expression.Constant(propertyValue);//创建常数
return Expression.Lambda<Func<T, bool>>(Expression.LessThanOrEqual(member, constant), parameter);
}

/// <summary>
/// 创建lambda表达式：p=>p.propertyName.Contains(propertyValue)
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="column"></param>
/// <param name="value"></param>
/// <returns></returns>
private static Expression<Func<T, bool>> GetContains<T>(string propertyName, string propertyValue)
{
ParameterExpression parameter = Expression.Parameter(typeof(T), "p");
MemberExpression member = Expression.PropertyOrField(parameter, propertyName);
MethodInfo method = typeof(string).GetMethod("Contains", new[] { typeof(string) });
ConstantExpression constant = Expression.Constant(propertyValue, typeof(string));
return Expression.Lambda<Func<T, bool>>(Expression.Call(member, method, constant), parameter);
}

/// <summary>
/// 创建lambda表达式：!(p=>p.propertyName.Contains(propertyValue))
/// </summary>
/// <typeparam name="T"></typeparam>
/// <param name="column"></param>
/// <param name="value"></param>
/// <returns></returns>
private static Expression<Func<T, bool>> GetNotContains<T>(string propertyName, string propertyValue)
{
ParameterExpression parameter = Expression.Parameter(typeof(T), "p");
MemberExpression member = Expression.PropertyOrField(parameter, propertyName);
MethodInfo method = typeof(string).GetMethod("Contains", new[] { typeof(string) });
ConstantExpression constant = Expression.Constant(propertyValue, typeof(string));
return Expression.Lambda<Func<T, bool>>(Expression.Not(Expression.Call(member, method, constant)), parameter);
}
/// <summary>
/// 组合And
/// </summary>
/// <returns></returns>
public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> first, Expression<Func<T, bool>> second)
{
return first.Compose(second, Expression.AndAlso);
}
/// <summary>
/// 组合Or
/// </summary>
/// <returns></returns>
public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> first, Expression<Func<T, bool>> second)
{
return first.Compose(second, Expression.OrElse);
}

/// <summary>
/// Combines the first expression with the second using the specified merge function.
/// </summary>
static Expression<T> Compose<T>(this Expression<T> first, Expression<T> second, Func<Expression, Expression, Expression> merge)
{
var map = first.Parameters
.Select((f, i) => new { f, s = second.Parameters[i] })
.ToDictionary(p => p.s, p => p.f);
var secondBody = ParameterRebinder.ReplaceParameters(map, second.Body);
return Expression.Lambda<T>(merge(first.Body, secondBody), first.Parameters);
}
/// <summary>
/// ParameterRebinder
/// </summary>
private class ParameterRebinder : ExpressionVisitor
{
/// <summary>
/// The ParameterExpression map
/// </summary>
readonly Dictionary<ParameterExpression, ParameterExpression> map;
/// <summary>
/// Initializes a new instance of the <see cref="ParameterRebinder"/> class.
/// </summary>
/// <param name="map">The map.</param>
ParameterRebinder(Dictionary<ParameterExpression, ParameterExpression> map)
{
this.map = map ?? new Dictionary<ParameterExpression, ParameterExpression>();
}
/// <summary>
/// Replaces the parameters.
/// </summary>
/// <param name="map">The map.</param>
/// <param name="exp">The exp.</param>
/// <returns>Expression</returns>
public static Expression ReplaceParameters(Dictionary<ParameterExpression, ParameterExpression> map, Expression exp)
{
return new ParameterRebinder(map).Visit(exp);
}
/// <summary>
/// Visits the parameter.
/// </summary>
/// <param name="p">The p.</param>
/// <returns>Expression</returns>
protected override Expression VisitParameter(ParameterExpression p)
{
ParameterExpression replacement;

if (map.TryGetValue(p, out replacement))
{
p = replacement;
}
return base.VisitParameter(p);
}
}