如何包含一个检查Property的And（）表达式及其值 [英] How to include an And() Expression that checks for a Property and it's value
问题描述
我想在我们的存储库中添加一个检查，用于在companyId上过滤所有对象，如果它在那里，并且匹配给定的值。
所以我们有：
public T First< T> （表达式< Func< T，bool>>表达式）其中T：EntityObject
{
var set = GetObjectSet< T>（）;
return set.FirstOrDefault< T>（）;
}
我想添加一些看起来像...
express.And（检查CompanyId属性是否存在，然后确保它= 3）;
有关如何解决这个问题的任何想法？
谢谢:)
如果您正在寻找一个功能，如果公司ID存在，您可以使用该功能来将公司id检查到您的表达式在实体上，这应该是诀窍：
public static Expression&FunC< T，bool>> CheckPropertyIfExists< T，TProperty>（表达式< Func< T，bool>>表达式，string propertyName，TProperty propertyValue）
{
Type type = typeof（T）;
var property = type.GetProperty（propertyName，typeof（TProperty））;
if（property == null ||！property.CanRead）
return expression;
return expression.Update（
Expression.And（//&&
Expression.Equal（// ==
Expression.MakeMemberAccess（expression.Parameters [0]，属性），// T参数。{propertyName}
Expression.Constant（propertyValue）//指定propertyValue常量
），
expression.Body //原始表达式
），
expression.Parameters
）;
}
您可以这样使用：
public T First< T>（表达式< Func< T，bool>>>表达式，int companyId）
{
var set = GetObjectSet< ; T>（）;
return set.FirstOrDefault< T>（CheckPropertyIfExists（expression，CompanyId，companyId））;
}
现在，您可以调用您的 First 方法与您的表达式和您要过滤的companyId。
一个稍微更好的方法是将其用作过滤方法，即将其重写为不需要内部表达式并可用于对象查询（或IQueryable）的扩展方法：
public静态ObjectQuery< T> FilterByPropertyIfExists< T，TProperty>（此ObjectQuery&T;查询，string propertyName，TProperty propertyValue）
{
Type type = typeof（T）;
var property = type.GetProperty（propertyName，typeof（TProperty））;
if（property == null ||！property.CanRead）
return query;
var parameter = Expression.Parameter（typeof（T），x）;
表达式< Func< T，bool>>> predicate =（Expression< Func< T，bool>）Expression.Lambda（
Expression.Equal（// ==
Expression.MakeMemberAccess（parameter，property），// T parameter。{propertyName }
Expression.Constant（propertyValue）//指定propertyValue常数
），
参数
）;
return query.Where（predicate）;
}
这样的美妙之处在于它会很好地与标准LINQ语法（查询和流畅）。
eg它允许这样的查询：
from x in repository.Clients.FilterByPropertyIfExists（Company，5）
where x == ???
select x.Name;
$ b $我已经清理了一下，并添加了一个参数可见性检查（必须是一个公共的静态属性），以及一个ObjectQuery实现（将自动用于ObjectQuery和ObjectSet）：
public static class QueryExtensions
{
public static IQueryable< T> FilterByPropertyIfExists< T，TProperty>（此IQueryable查询，string propertyName，TProperty propertyValue）
{
类型type = typeof（T）;
var property = type.GetProperty（
propertyName，
BindingFlags.Instance | BindingFlags.Public，//必须是公共实例属性
null，
typeof（TProperty ），//必须是正确的返回类型
Type.EmptyTypes，//不能有参数
null
）;
if（property == null ||！property.CanRead）//必须存在且可读
return query; //返回查询不变
//创建一个谓词传递给Where方法
var parameter = Expression.Parameter（typeof（T），it）;
表达式< Func< T，bool>>> predicate =（Expression< Func< T，bool>）Expression.Lambda（
Expression.Equal（// ==
Expression.MakeMemberAccess（parameter，property），// T parameter。{propertyName }
Expression.Constant（propertyValue）//指定propertyValue常数
），
参数
）;
return query.Where（predicate）; //过滤查询
}
public static ObjectQuery< T> FilterByPropertyIfExists< T，TProperty>（此ObjectQuery&T;查询，string propertyName，TProperty propertyValue）
{
var filteredQuery = FilterByPropertyIfExists（（IQueryable ））查询，propertyName，propertyValue）;
return（ObjectQuery< T>）filteredQuery; //将已过滤的查询转换为ObjectQuery
}
}
I'd like to add a check in our repository that filters all objects out on a companyId if it's there and if it matches a given value.
So where we have:
public T First<T>(Expression<Func<T, bool>> expression) where T : EntityObject
{
var set = GetObjectSet<T>();
return set.FirstOrDefault<T>();
}
I would like to add line which looks something where...
express.And("Check for CompanyId property if it exists then make sure it = 3");
Any ideas on how to go about this?
Thanks :)
If you're looking for a function which you can use to tack on a company id check to your expression if a company id exists on the entity, this should do the trick:
public static Expression<Func<T, bool>> CheckPropertyIfExists<T, TProperty>(Expression<Func<T, bool>> expression, string propertyName, TProperty propertyValue)
{
Type type = typeof(T);
var property = type.GetProperty(propertyName, typeof(TProperty));
if(property == null || !property.CanRead)
return expression;
return expression.Update(
Expression.And( // &&
Expression.Equal( // ==
Expression.MakeMemberAccess(expression.Parameters[0], property), // T parameter.{propertyName}
Expression.Constant(propertyValue) // specified propertyValue constant
),
expression.Body // Original expression
),
expression.Parameters
);
}
You could use it like this:
public T First<T>(Expression<Func<T, bool>> expression, int companyId)
{
var set = GetObjectSet<T>();
return set.FirstOrDefault<T>(CheckPropertyIfExists(expression, "CompanyId", companyId));
}
And now you can call your First method with your expression and the companyId you want to filter by.
A slightly better way to do this might be to use it as a filtering method, i.e. rewrite it as an extension method that doesn't require an inner expression and works on an object query (or IQueryable):
public static ObjectQuery<T> FilterByPropertyIfExists<T, TProperty>(this ObjectQuery<T> query, string propertyName, TProperty propertyValue)
{
Type type = typeof(T);
var property = type.GetProperty(propertyName, typeof(TProperty));
if(property == null || !property.CanRead)
return query;
var parameter = Expression.Parameter(typeof(T), "x");
Expression<Func<T, bool>> predicate = (Expression<Func<T, bool>>)Expression.Lambda(
Expression.Equal( // ==
Expression.MakeMemberAccess(parameter, property), // T parameter.{propertyName}
Expression.Constant(propertyValue) // specified propertyValue constant
),
parameter
);
return query.Where(predicate);
}
The beauty of this is that it will work really nicely with the stanard LINQ syntaxes (both query and fluent).
e.g. it allows queries like this:
from x in repository.Clients.FilterByPropertyIfExists("Company", 5)
where x == ???
select x.Name;
[EDIT]
I've cleaned it up a bit and added a check on parameter visibility (must be a public, static property), as well as an ObjectQuery implementation (which will be automatically used for ObjectQuery and ObjectSet):
public static class QueryExtensions
{
public static IQueryable<T> FilterByPropertyIfExists<T, TProperty>(this IQueryable<T> query, string propertyName, TProperty propertyValue)
{
Type type = typeof(T);
var property = type.GetProperty(
propertyName,
BindingFlags.Instance | BindingFlags.Public, // Must be a public instance property
null,
typeof(TProperty), // Must be of the correct return type
Type.EmptyTypes, // Can't have parameters
null
);
if (property == null || !property.CanRead) // Must exist and be readable
return query; // Return query unchanged
// Create a predicate to pass to the Where method
var parameter = Expression.Parameter(typeof(T), "it");
Expression<Func<T, bool>> predicate = (Expression<Func<T, bool>>)Expression.Lambda(
Expression.Equal( // ==
Expression.MakeMemberAccess(parameter, property), // T parameter.{propertyName}
Expression.Constant(propertyValue) // specified propertyValue constant
),
parameter
);
return query.Where(predicate); // Filter the query
}
public static ObjectQuery<T> FilterByPropertyIfExists<T, TProperty>(this ObjectQuery<T> query, string propertyName, TProperty propertyValue)
{
var filteredQuery = FilterByPropertyIfExists((IQueryable<T>)query, propertyName, propertyValue);
return (ObjectQuery<T>)filteredQuery; // Cast filtered query back to an ObjectQuery
}
}
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