如何动态拼接出.Where(c => List.Contains(c.Id));
0
悬赏园豆：10
[已解决问题]
解决于 2018-12-12 14:47
实现了一个==的拼接 不知道怎么实现Contains的拼接：
public static IQueryable<T> WhereEqual<T>(this IQueryable<T> q, string fieldName, string fieldValue)
{
Type t = typeof(T);
ParameterExpression param = Expression.Parameter(t, "c");
Expression left = Expression.Property(param, t.GetProperty(fieldName));
Expression right = Expression.Constant(fieldValue);
//Expression.
Expression filter = Expression.Equal(left, right);
Expression pred = Expression.Lambda(filter, param);
Expression expr = Expression.Call(typeof(Queryable), "Where", new Type[] { t }, Expression.Constant(q), pred);
return q.Provider.CreateQuery<T>(expr);
}
最佳答案
1
参考 How do I create an expression tree to represent 'String.Contains(“term”)' in C#? ：
static Expression<Func<T, bool>> GetExpression<T>(string propertyName, string propertyValue)
{
var parameterExp = Expression.Parameter(typeof(T), "type");
var propertyExp = Expression.Property(parameterExp, propertyName);
MethodInfo method = typeof(string).GetMethod("Contains", new[] { typeof(string) });
var someValue = Expression.Constant(propertyValue, typeof(string));
var containsMethodExp = Expression.Call(propertyExp, method, someValue);
return Expression.Lambda<Func<T, bool>>(containsMethodExp, parameterExp);
}
收获园豆：10
感谢 我试试能不能再EF中使用
其他回答(1)
0
public Expression<Func<TEntity, bool>> ContainsPredicate<TEntity, T>(T[] arr, string fieldname) where TEntity : class {
ParameterExpression entity = Expression.Parameter(typeof(TEntity), "entity");
MemberExpression member = Expression.Property(entity, fieldname);
var containsMethods = typeof(Enumerable).GetMethods(BindingFlags.Static | BindingFlags.Public)
.Where(m => m.Name == "Contains");
MethodInfo method = null;
foreach (var m in containsMethods) {
if (m.GetParameters().Count() == 2) {
method = m;
break;
}
}
method = method.MakeGenericMethod(member.Type);
var exprContains = Expression.Call(method, new Expression[] { Expression.Constant(arr), member });
return Expression.Lambda<Func<TEntity, bool>>(exprContains, entity);
}
