This is a ASP.NET MVC project.
I want to query a database table with a specific value of a textbox from the view.
This queries two fields:
public ActionResult Index(string search)
{
return View(db.KDtable
.Where(x =>
x.Name.StartsWith(search)
|| x.Description.StartsWith(search)
|| search == null)
.ToList()
);
}
string search is the value of the textbox.
Question:
How can I, instead of adding all fields manually to the lambda expression e.g. x.City.StartsWith(search), just plain and simple query all the table fields with the input from the textbox.
Thx
Try this:
public static Expression<Func<T,bool>> CreateTextSearch<T>(string searchText)
{
Type t = typeof(T);
var props = t.GetProperties().Cast<PropertyInfo>().Where(p => p.PropertyType == typeof(string));
var searchTextExpr = Expression.Constant(searchText);
var tParameterExpr = Expression.Parameter(typeof(T));
Expression expr = null;
foreach(var prop in props)
{
var criteria = Expression.Call(
Expression.Property(tParameterExpr, prop),
typeof(string).GetMethod("StartsWith", new Type[] { typeof(string) }),
searchTextExpr);
if(expr == null)
expr = criteria;
else
expr = Expression.Or(expr, criteria);
}
return Expression.Lambda<Func<T,bool>>(expr, tParameterExpr);
}
call it like this: MySet.Where(CreateTextSearch<MyType>("DDD")); for IQueryables and MySet.Where(CreateTextSearch<MyType>("DDD").Compile()); for regular IEnumerables.
Related
I am trying to build a filter method for IQueryable Type,
I could achieve this for ex:
query = query.Filter(UsersListId, e => e.UserId);
public static IQueryable<T> Filter<T, TSearch>(this IQueryable<T> query, List<TSearch> list, Expression<Func<T, TSearch>> props)
{
if (list == null || list.Count == 0)
{
return query;
}
var propertyPath = props.Body.ToString().Replace(props.Parameters[0] + ".", string.Empty);
var containsMethod = typeof(List<TSearch>).GetMethod("Contains", new Type[] { typeof(TSearch) });
ConstantExpression constlist = Expression.Constant(list);
var param = Expression.Parameter(typeof(T), "Entity");
var newvalue = GetPropertyValue(param, propertyPath);
var body = Expression.Call(constlist, containsMethod, newvalue);
var exp = Expression.Lambda<Func<T, bool>>(body, param);
return query.Where(exp);
}
public static MemberExpression GetPropertyValue(ParameterExpression parExp, string propertyPath)
{
var properties = propertyPath.Split('.').ToArray();
var value = Expression.Property(parExp, properties[0]);
for (int i = 1; i < properties.Length; i++)
{
value = Expression.Property(value, properties[i]);
}
return value;
}
this code takes the propertyPath (ex: x.User.Department.Id)
and returns the value,
The problems here:
I cannot pass a nullable object if the list isn't nullable too
I am not quite sure weather it's the right way to access properties
so my question is what is the solution for these problems?
I am trying to build an expression tree dynamically to fetch data from a database.
The following codes are used for this.
Expression<Func<Client, bool>> expression = x => true;
foreach (var item in searchParams)
{
var operatorType = ExpressionType.Equal;
string propertyName = null;
object value = null;
string keyValue = item.Value;
if (item.Key == Constants.SearchParameterNames.Id)
{
int val = 0;
if (int.TryParse(keyValue, out val))
value = val;
propertyName = "ClientID";
}
else if (item.Key == Constants.SearchParameterNames.Lastupdate)
{
DateTime dateTime;
if (DateTime.TryParse(keyValue, out dateTime))
value = dateTime;
propertyName = "LastChange";
}
if (!string.IsNullOrWhiteSpace(propertyName) && value != null)
{
var exp = GetBinaryOperation<Client>(propertyName, operatorType, value);
var exp1 = Expression.And(expression.Body, exp);
expression = Expression.Lambda<Func<Client, bool>>(exp1, expression.Parameters);
}
}
var client = _clientRepository.FindBy(expression).ToList();
when _clientRepository.FindBy(expression).ToList() is executed I am getting an exception of
The parameter 'x' was not bound in the specified LINQ to Entities
query expression.
The method used to create expression:
public BinaryExpression GetBinaryOperation<T>(string propertyName, ExpressionType type, object value)
{
var parameterExpression = Expression.Parameter(typeof(T), "x");
var memberExpression = Expression.Property(parameterExpression, propertyName);
var propertyType = GetMemberType(memberExpression);
var rhs = Expression.Constant(value);
var binaryExpression = Expression.MakeBinary(type, memberExpression, rhs);
return binaryExpression;
}
When building such an expression you have to preserve the top-level parameter expression instance. When you create a new parameter expression in the GetBinaryOperation function, that will be a different instance (hence the not bound term), regardless of the fact that its name is the same "x".
Instead of creating a new parameter instance, you should pass the original LambdaExpression's "x" parameter to the GetBinaryOperation function using for example expression.Parameters[0].
All in all, you have to use the same parameter expression instance throughout the entire expression tree in this case.
I have a list which I need to order eg.
var list = someelements;
I also have a parameter which says by which property and what direction I should order list data eg.
var sortby = "Name";
var sortdirection = "desc";
I was wondering if I can match string property name with the right property so I get:
var list = someelements.OrderBy(x => x.Name).ToList();
when sortby == "Name" without the need of using switch loop to check property name and assign a correct property to OrderBy.
Same I would like to achieve with select either OrderBy or OrderByDescending depending whether I get sortdirection = "asc" or sortdirection = "desc"
Is it possible and if yes, how?
You can get Dynamic Linq through Nuget. Then you can use .OrderBy(sortby + " " + sortdirection).
Here is the link: Dynamic Linq.
Here is one solution that does not use Dynamic Linq:
public class Helper
{
public static IEnumerable<T> OrderByDynamic<T>(IEnumerable<T> items, string sortby, string sort_direction)
{
var property = typeof (T).GetProperty(sortby);
var result = typeof(Helper)
.GetMethod("OrderByDynamic_Private", BindingFlags.NonPublic | BindingFlags.Static)
.MakeGenericMethod(typeof (T), property.PropertyType)
.Invoke(null, new object[]{ items, sortby, sort_direction});
return (IEnumerable<T>)result;
}
private static IEnumerable<T> OrderByDynamic_Private<T,TKey>(IEnumerable<T> items, string sortby, string sort_direction)
{
var parameter = Expression.Parameter(typeof (T), "x");
Expression<Func<T, TKey>> property_access_expression =
Expression.Lambda<Func<T, TKey>>(
Expression.Property(parameter, sortby),
parameter);
if (sort_direction == "asc")
{
return items.OrderBy(property_access_expression.Compile());
}
if (sort_direction == "desc")
{
return items.OrderByDescending(property_access_expression.Compile());
}
throw new Exception("Invalid Sort Direction");
}
}
You can use it like this:
var result = Helper.OrderByDynamic(list, "Name", "desc").ToList();
I am trying to build a Lambda Expression for a table that has been created at run time.
The Expression is build fine but when I call Compile() method I get this error
"ParameterExpression of type 'cseval.Item' cannot be used for delegate parameter of type 'System.Object'"
this is my function
public Func<dynamic, Boolean> GetWhereExp(List<WhereCondition> SearchFieldList, dynamic item)
{
ParameterExpression pe = Expression.Parameter(item.GetType(), "c");
Expression combined = null;
if (SearchFieldList != null)
{
foreach (WhereCondition fieldItem in SearchFieldList)
{
//Expression for accessing Fields name property
Expression columnNameProperty = Expression.Property(pe, fieldItem.ColumName);
//the name constant to match
Expression columnValue = Expression.Constant(fieldItem.Value);
//the first expression: PatientantLastName = ?
Expression e1 = Expression.Equal(columnNameProperty, columnValue);
if (combined == null)
{
combined = e;
}
else
{
combined = Expression.And(combined, e);
}
}
}
var result = Expression.Lambda<Func<dynamic, bool>>(combined, pe);
return result.Compile();
}
I've changed dynamic to generics, this code works for me:
public Func<T, Boolean> GetWhereExp<T>(List<WhereCondition> SearchFieldList, T item)
{
var pe = Expression.Parameter(item.GetType(), "c");
Expression combined = null;
if (SearchFieldList != null)
{
foreach (var fieldItem in SearchFieldList)
{
var columnNameProperty = Expression.Property(pe, fieldItem.ColumName);
var columnValue = Expression.Constant(fieldItem.Value);
var e1 = Expression.Equal(columnNameProperty, columnValue);
combined = combined == null ? e1 : Expression.And(combined, e1);
}
}
var result = Expression.Lambda<Func<T, bool>>(combined, pe);
return result.Compile();
}
Small remark: your method returns function, not an expression, so the name 'GetWhereExp' is slightly incorrect. If you want to return function, imho, it's better to use reflection.
UPD: I use this code to test:
var expressions = new List<WhereCondition>
{
new WhereCondition("Column1", "xxx"),
new WhereCondition("Column2", "yyy"),
};
var item = new
{
Column1 = "xxx",
Column2 = "yyy"
};
var func = LinqExpr.GetWhereExp(expressions, (dynamic)item);
Console.WriteLine(new[] {item}.Count(a => func(a)));
I'm using Entity Framework and building queries using navigation properties dynamically.
For most of my use cases, the following works fine:
private static MethodCallExpression GetNavigationPropertyExpression<T>(string propertyName, int test,
ParameterExpression parameter, string subParameter)
{
var navigationPropertyCollection = Expression.Property(parameter, propertyName);
var childType = navigationPropertyCollection.Type.GetGenericArguments()[0];
var anyMethod = typeof(Enumerable).GetMethods().Single(m => m.Name == "Any" && m.GetParameters().Length == 2).MakeGenericMethod(childType);
var aclAttribute = GetAclAttribute(typeof(T), propertyName);
var childProperty = aclAttribute.ChildProperty;
var propertyCollectionGenericArg = childType;
var serviceLocationsParam = Expression.Parameter(propertyCollectionGenericArg, subParameter);
var left = Expression.Property(serviceLocationsParam, childProperty);
var right = Expression.Constant(test, typeof(int));
var isEqual = Expression.Equal(left, right);
var subLambda = Expression.Lambda(isEqual, serviceLocationsParam);
var resultExpression = Expression.Call(anyMethod, navigationPropertyCollection, subLambda);
return resultExpression;
}
I use a custom AclAttribute class assigned to properties via metadata type and partial classes. For navigation properties, a ChildProperty is provided so that the expression builder knows to look deeper for the desired property.
For example: the table Services references another table called ServiceLocations. I need the LocationId value(s) from the ServiceLocations reference. This part works fine.
My problem is when there is more than 1 nested property to go through. Another example: the table ServiceCategories references Services which, again, references ServiceLocations. Like before, I need the LocationId value(s) from ServiceLocations.
I've done this manually by using two "Any" methods, combining, and returning the resulting expression, but there will be times where navigation properties won't be collections, or a child of a navigation property may be a collection. For those cases, I need some kind of recursive option. I've been trying for a while now, and coming up short.
Since I mentioned it, here's the test method I put together for my second example. This works, but I'm violating DRY. (Note: I didn't name the tables):
private static MethodCallExpression GetNestedNavigationPropertyExpression(int test, ParameterExpression rootParameter)
{
var servicesProperty = Expression.Property(rootParameter, "tblServices");
var servicesParameter = Expression.Parameter(servicesProperty.Type.GetGenericArguments()[0], "ss");
var serviceLocationsProperty = Expression.Property(servicesParameter, "tblServiceLocations");
var serviceLocationsParameter = Expression.Parameter(serviceLocationsProperty.Type.GetGenericArguments()[0], "s");
var servicesAnyMethod = typeof(Enumerable).GetMethods().Single(m => m.Name == "Any" && m.GetParameters().Length == 2).MakeGenericMethod(servicesProperty.Type.GetGenericArguments()[0]);
var serviceLocationsAnyMethod = typeof(Enumerable).GetMethods().Single(m => m.Name == "Any" && m.GetParameters().Length == 2).MakeGenericMethod(serviceLocationsProperty.Type.GetGenericArguments()[0]);
var aclAttribute = GetAclAttribute(typeof(tblService), "tblServiceLocations");
var left = Expression.Property(serviceLocationsParameter, aclAttribute.ChildProperty);
var right = Expression.Constant(test, typeof(int));
var isEqual = Expression.Equal(left, right);
var subLambda = Expression.Lambda(isEqual, serviceLocationsParameter);
var endExpression = Expression.Call(serviceLocationsAnyMethod, serviceLocationsProperty, subLambda);
var intermediaryLamba = Expression.Lambda(endExpression, servicesParameter);
var resultExpression = Expression.Call(servicesAnyMethod, servicesProperty, intermediaryLamba);
return resultExpression;
}
With this it should be possible to build your queries:
public static Expression GetNavigationPropertyExpression(Expression parameter, int test, params string[] properties)
{
Expression resultExpression = null;
Expression childParameter, navigationPropertyPredicate;
Type childType = null;
if (properties.Count() > 1)
{
//build path
parameter = Expression.Property(parameter, properties[0]);
var isCollection = typeof(IEnumerable).IsAssignableFrom(parameter.Type);
//if it´s a collection we later need to use the predicate in the methodexpressioncall
if (isCollection)
{
childType = parameter.Type.GetGenericArguments()[0];
childParameter = Expression.Parameter(childType, childType.Name);
}
else
{
childParameter = parameter;
}
//skip current property and get navigation property expression recursivly
var innerProperties = properties.Skip(1).ToArray();
navigationPropertyPredicate = GetNavigationPropertyExpression(childParameter, test, innerProperties);
if (isCollection)
{
//build methodexpressioncall
var anyMethod = typeof(Enumerable).GetMethods().Single(m => m.Name == "Any" && m.GetParameters().Length == 2);
anyMethod = anyMethod.MakeGenericMethod(childType);
navigationPropertyPredicate = Expression.Call(anyMethod, parameter, navigationPropertyPredicate);
resultExpression = MakeLambda(parameter, navigationPropertyPredicate);
}
else
{
resultExpression = navigationPropertyPredicate;
}
}
else
{
//Formerly from ACLAttribute
var childProperty = parameter.Type.GetProperty(properties[0]);
var left = Expression.Property(parameter, childProperty);
var right = Expression.Constant(test, typeof(int));
navigationPropertyPredicate = Expression.Equal(left, right);
resultExpression = MakeLambda(parameter, navigationPropertyPredicate);
}
return resultExpression;
}
private static Expression MakeLambda(Expression parameter, Expression predicate)
{
var resultParameterVisitor = new ParameterVisitor();
resultParameterVisitor.Visit(parameter);
var resultParameter = resultParameterVisitor.Parameter;
return Expression.Lambda(predicate, (ParameterExpression)resultParameter);
}
private class ParameterVisitor : ExpressionVisitor
{
public Expression Parameter
{
get;
private set;
}
protected override Expression VisitParameter(ParameterExpression node)
{
Parameter = node;
return node;
}
}
Call it like:
var parameter = Expression.Parameter(typeof(A), "A");
var expression = ExpressionBuilder.GetNavigationPropertyExpression(parameter, 8,"CollectionOfB", "CollectionOfC", "ID");