Net Core:查找 Class 中任何变量字段的数据类型
Net Core: Find Data Type for any Variable Field in Class
我如何获取这个 OrderBy 表达式树并使其接受任何订单类型、int、float、string、boolean 等?可能吗?现在它的类型转换为仅字符串。我应该在调用方法时将所有内容都转换为字符串,还是有更好的方法使它更通用?
我只需要 classT 中这个 propertyName 的数据类型,所以我可以放在下面的函数中。测试这些,还没有运气。
会员类型,
获取类型(),
字段类型
正在创建表达式:
public static class ExpressionTreesExtesion
{
public static Expression<Func<T,string>> OrderByExpression<T>(this IEnumerable<T> enumerable, string propertyName)
{
var propInfo = typeof(T).GetProperty(propertyName);
var collectionType = typeof(T);
var parameterExpression = Expression.Parameter(collectionType, "x");
var propertyAccess = Expression.MakeMemberAccess(parameterExpression, propInfo);
var orderExpression = Expression.Lambda<Func<T,string>>(propertyAccess, parameterExpression);
return orderExpression;
}
}
如何调用:
var ProductExpression = records.OrderByExpression("Name");
var result = records.OrderBy(ProductExpression.Compile());
ProductExpression.Compile() above will compile into x => x.Name, where column name is supplied at the run-time
因为类型在编译时是未知的,你将不能使用像 Expression<Func<T,TKey>>
.
这样的强类型 return 类型
public static class ExpressionTreesExtension {
static readonly Type funcTTResult = typeof(Func<,>);
public static IOrderedQueryable<T> OrderByProperty<T>(this IEnumerable<T> enumerable, string propertyName) {
var itemType = typeof(T);
var propertyInfo = itemType.GetProperty(propertyName);
var propertyType = propertyInfo.PropertyType;
// Func<T,TPropertyType>
var delegateType = funcTTResult.MakeGenericType(itemType, propertyType);
// T x =>
var parameterExpression = Expression.Parameter(itemType, "x");
// T x => x.Property
var propertyAccess = Expression.Property(parameterExpression, propertyInfo);
// Func<T,TPropertyType> = T x => x.Property
var keySelector = Expression.Lambda(delegateType, propertyAccess, parameterExpression);
var query = enumerable.AsQueryable();
// query.OrderBy(x => x.Property)
MethodCallExpression orderByExpression = Expression.Call(
typeof(Queryable),
"OrderBy",
new[] { query.ElementType, propertyInfo.PropertyType },
query.Expression, keySelector);
// Create an executable query from the expression tree.
return (IOrderedQueryable<T>)query.Provider.CreateQuery<T>(orderByExpression);
}
}
引用How to: Use Expression Trees to Build Dynamic Queries (C#)
并且喜欢使用
//IEnumerable<Person> records...
var data = records.OrderByProperty("Name");
我如何获取这个 OrderBy 表达式树并使其接受任何订单类型、int、float、string、boolean 等?可能吗?现在它的类型转换为仅字符串。我应该在调用方法时将所有内容都转换为字符串,还是有更好的方法使它更通用?
我只需要 classT 中这个 propertyName 的数据类型,所以我可以放在下面的函数中。测试这些,还没有运气。
会员类型, 获取类型(), 字段类型
正在创建表达式:
public static class ExpressionTreesExtesion
{
public static Expression<Func<T,string>> OrderByExpression<T>(this IEnumerable<T> enumerable, string propertyName)
{
var propInfo = typeof(T).GetProperty(propertyName);
var collectionType = typeof(T);
var parameterExpression = Expression.Parameter(collectionType, "x");
var propertyAccess = Expression.MakeMemberAccess(parameterExpression, propInfo);
var orderExpression = Expression.Lambda<Func<T,string>>(propertyAccess, parameterExpression);
return orderExpression;
}
}
如何调用:
var ProductExpression = records.OrderByExpression("Name");
var result = records.OrderBy(ProductExpression.Compile());
ProductExpression.Compile() above will compile into x => x.Name, where column name is supplied at the run-time
因为类型在编译时是未知的,你将不能使用像 Expression<Func<T,TKey>>
.
public static class ExpressionTreesExtension {
static readonly Type funcTTResult = typeof(Func<,>);
public static IOrderedQueryable<T> OrderByProperty<T>(this IEnumerable<T> enumerable, string propertyName) {
var itemType = typeof(T);
var propertyInfo = itemType.GetProperty(propertyName);
var propertyType = propertyInfo.PropertyType;
// Func<T,TPropertyType>
var delegateType = funcTTResult.MakeGenericType(itemType, propertyType);
// T x =>
var parameterExpression = Expression.Parameter(itemType, "x");
// T x => x.Property
var propertyAccess = Expression.Property(parameterExpression, propertyInfo);
// Func<T,TPropertyType> = T x => x.Property
var keySelector = Expression.Lambda(delegateType, propertyAccess, parameterExpression);
var query = enumerable.AsQueryable();
// query.OrderBy(x => x.Property)
MethodCallExpression orderByExpression = Expression.Call(
typeof(Queryable),
"OrderBy",
new[] { query.ElementType, propertyInfo.PropertyType },
query.Expression, keySelector);
// Create an executable query from the expression tree.
return (IOrderedQueryable<T>)query.Provider.CreateQuery<T>(orderByExpression);
}
}
引用How to: Use Expression Trees to Build Dynamic Queries (C#)
并且喜欢使用
//IEnumerable<Person> records...
var data = records.OrderByProperty("Name");