动态LINQ喜欢 [英] Dynamic LINQ Like
问题描述
如何为编写一个动态的linq方法,就像
子句一样。
为了参考,在IEnumerable上有动态LINQ OrderBy T> 。我正在寻找一个类似的动态像
子句。
For reference, there is Dynamic LINQ OrderBy on IEnumerable<T>. I am looking for a similar one for dynamic Like
clause.
我有以下扩展方法,如: / p>
I have the following extension methods for like:
public static IQueryable<T> Like<T>(this IQueryable<T> source, string propertyName,
string keyword)
{
var type = typeof(T);
var property = type.GetProperty(propertyName);
var parameter = Expression.Parameter(type, "p");
var propertyAccess = Expression.MakeMemberAccess(parameter, property);
var constant = Expression.Constant("%" + keyword + "%");
var methodExp = Expression.Call(
null,
typeof(SqlMethods).GetMethod("Like", new[] { typeof(string), typeof(string) }),
propertyAccess,
constant);
var lambda = Expression.Lambda<Func<T, bool>>(methodExp, parameter);
return source.Where(lambda);
}
上述方法给出错误
方法'Boolean Like(System.String,System.String)'不能在客户端上使用;它只适用于SQL的翻译。
Method 'Boolean Like(System.String, System.String)' cannot be used on the client; it is only for translation to SQL.
另一种方法是从动态LINQ OrderBy on IEnumerable< T> :
public static IQueryable<T> ALike<T>(this IQueryable<T> source, string property,
string keyword)
{
string[] props = property.Split('.');
Type type = typeof(T);
ParameterExpression arg = Expression.Parameter(type, "x");
Expression expr = arg;
foreach (string prop in props)
{
// use reflection (not ComponentModel) to mirror LINQ
PropertyInfo pi = type.GetProperty(prop);
expr = Expression.Property(expr, pi);
type = pi.PropertyType;
}
var constant = Expression.Constant("%" + keyword + "%");
var methodExp = Expression.Call(
null,
typeof(SqlMethods).GetMethod("Like", new[] { typeof(string), typeof(string) }),
expr,
constant);
Type delegateType = typeof(Func<,>).MakeGenericType(typeof(T), type);
LambdaExpression lambda = Expression.Lambda(delegateType, methodExp, arg);
object result = typeof(Queryable).GetMethods().Single(
method => method.IsGenericMethodDefinition
&& method.GetGenericArguments().Length == 2
&& method.GetParameters().Length == 2)
.MakeGenericMethod(typeof(T), type)
.Invoke(null, new object[] { source, lambda });
return (IQueryable<T>)result;
}
上述方法给出错误:
类型System.Boolean的表达式不能用于返回类型System.String
Expression of type 'System.Boolean' cannot be used for return type 'System.String'
任何想法?
推荐答案
某些东西:
static void Main() {
using(var ctx= new DataClasses1DataContext()) {
ctx.Log = Console.Out;
var qry = ctx.Customers.WhereLike("CompanyName", "a%s");
Console.WriteLine(qry.Count());
}
}
static IQueryable<T> WhereLike<T>(this IQueryable<T> source,
string propertyOrFieldName, string pattern) {
var param = Expression.Parameter(typeof(T), "row");
var body = Expression.Call(
null,
typeof(SqlMethods).GetMethod("Like",
new[] { typeof(string), typeof(string) }),
Expression.PropertyOrField(param, propertyOrFieldName),
Expression.Constant(pattern, typeof(string)));
var lambda = Expression.Lambda<Func<T, bool>>(body, param);
return source.Where(lambda);
}
static IQueryable<T> WhereLike<T>(this IQueryable<T> source,
string propertyOrFieldName, string pattern, char escapeCharacter) {
var param = Expression.Parameter(typeof(T), "row");
var body = Expression.Call(
null,
typeof(SqlMethods).GetMethod("Like",
new[] { typeof(string), typeof(string), typeof(char) }),
Expression.PropertyOrField(param, propertyOrFieldName),
Expression.Constant(pattern, typeof(string)),
Expression.Constant(escapeCharacter,typeof(char)));
var lambda = Expression.Lambda<Func<T, bool>>(body, param);
return source.Where(lambda);
}
您还可以考虑使其更可重复使用:
You might also consider making it more reusable:
static void Main() {
using(var ctx= new DataClasses1DataContext()) {
ctx.Log = Console.Out;
var qry1 = ctx.Customers.WhereInvoke<Customer, string>(
"CompanyName", s => s.Contains("abc"));
Console.WriteLine(qry1.Count());
var qry2 = ctx.Customers.WhereInvoke<Customer, string>(
"CompanyName", s => s.StartsWith("abc"));
Console.WriteLine(qry2.Count());
var qry3 = ctx.Customers.WhereInvoke<Customer, string>(
"CompanyName", s => s.EndsWith("abc"));
Console.WriteLine(qry3.Count());
}
}
static IQueryable<TSource> WhereInvoke<TSource, TValue>(
this IQueryable<TSource> source,
string propertyOrFieldName,
Expression<Func<TValue, bool>> func) {
var param = Expression.Parameter(typeof(TSource), "row");
var prop = Expression.PropertyOrField(param, propertyOrFieldName);
if(prop.Type != typeof(TValue)) {
throw new InvalidOperationException("The property must be " + typeof(TValue).Name);
}
var body = Expression.Invoke(func, prop);
var lambda = Expression.Lambda<Func<TSource, bool>>(body, param);
return source.Where(lambda);
}
这篇关于动态LINQ喜欢的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!