我想使用通用搜索参数创建用于分页的通用类。我使用反射来获取滤镜属性。可以使用我不太了解的表达式来实现。任何帮助将不胜感激。
public IEnumerable<T> ModelPagination(F filters) <-- F class filter properties eg. Name, CNIC for search
{
Type C = Type.GetType("filters");
PropertyInfo[] properties = C.GetProperties();
foreach (PropertyInfo prop in properties)
{
prop.Name;
}
return dbEntity.Where(x => ...... ).ToList(); <--- want to pass each property as lambda for something like x -> x.Name == filters.Name || filters.Name == Null
}
答案 0 :(得分:2)
这将构建lambda表达式,该表达式将与通用类型T
和Filter
类之间的属性相交,并比较它们的相等性,而且每个单独的属性对都与AND条件组合。
public static IEnumerable<T> ModelPagination<T>(F filter)
{
// all properties which are in the fiter class also present in the generic type T
var commonPropertyNames = filter
.GetType()
.GetProperties(BindingFlags.Instance | BindingFlags.Public)
.Select(x => x.Name)
.Intersect(
typeof(T)
.GetProperties(BindingFlags.Instance | BindingFlags.Public)
.Select(x => x.Name)
);
var argumentExpression = Expression.Parameter(typeof(T), "x");
var filterConstantExpression = Expression.Constant(filter);
// build the expression
var expression = (BinaryExpression)null;
foreach (var propertyName in commonPropertyNames)
{
var filterPropertyExpression = Expression.Property(filterConstantExpression, propertyName);
var equalExpression = Expression.Equal(
Expression.Property(argumentExpression, propertyName),
filterPropertyExpression
);
var nullCheckExpression = Expression.Equal(
filterPropertyExpression,
Expression.Constant(null)
);
var orExpression = Expression.OrElse(equalExpression, nullCheckExpression);
if (expression == null)
{
expression = orExpression;
}
else
{
expression = Expression.AndAlso(expression, orExpression);
}
}
var lambda = Expression.Lambda<Func<T, bool>>(expression, argumentExpression);
return dbContext.Entry<T>().Where(lambda).ToList();
}
如果您拥有T
这样的{ FirstName, LastName }
类型和Filter
这样的{ FirstName }
类
它将创建以下表达式
x => x.FirstName == filter.FirstName || filter.FirstName == null
如果您拥有T
这样的{ FirstName, LastName }
类型和Filter
这样的{ FirstName, LastName }
类
它将创建以下表达式
x => (x.FirstName == filter.FirstName || filter.FirstName == null)
&& (x.LastName == filter.LastName || filter.LastName == null)
这可以完成工作,但是还有优化的空间。