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LINQ with dynamic where clause in EFCore

I'm using net5.0 and EntityFrameworkCore 5.0.4.
I have a search method that has optional strings to search for on a DataContext in EFCore.
I want to check if each of the strings is not null or white space.
I could do this:
var query = context.Model.AsQueryable();
if (!string.IsNullOrWhiteSpace(parameters.Id))
{
query = query.Where(x => x.Id.ToLower().Contains(parameters.Id.ToLower()));
}
but that is just horrible to maintain. What I started trying to get going is this:
public static IQueryable<T> FilterBy<T>(this IQueryable<T> query, string? searchValue,
Expression<Func<T, string>> getValueExpression)
{
if (string.IsNullOrWhiteSpace(searchValue?.Trim()))
{
return query;
}
// return with a where clause
}
I got this working but it does not support accessing joins that I need and I get the feeling this is not a good way:
var searchLower = searchValue.Trim().ToLower();
var propertyName = getValueExpression.GetMemberAccess().Name;
return query.Where(x => EF.Property<string?>(x!, propertyName)!.ToLower().Contains(searchLower));
I want to use it like so:
query
.FilterBy(parameters.Id, x => x.Id)
.FilterBy(parameters.Name, x => x.Name)
.FilterBy(parameters.CompanyName, x => x.Company.Name) // access via include/join
Solution
private static readonly MethodInfo StringContainsMethod =
typeof(string).GetMethod(nameof(string.Contains), new[] {typeof(string)})!;
private static readonly MethodInfo StringToLowerMethod =
typeof(string).GetMethod(nameof(string.ToLower), Type.EmptyTypes)!;
public static IQueryable<T> FilterBy<T>(this IQueryable<T> query, string? searchValue,
Expression<Func<T, string?>> memberExpression)
{
if (string.IsNullOrWhiteSpace(searchValue))
return query;
var valueExpression = Expression.Constant(searchValue.ToLower());
var toLower = Expression.Call(memberExpression.Body, StringToLowerMethod);
var call = Expression.Call(toLower, StringContainsMethod, valueExpression);
var sourceParam = memberExpression.Parameters.First();
Expression<Func<T, bool>> predicate = Expression.Lambda<Func<T, bool>>(call, sourceParam);
return query.Where(predicate);
}
Integer
public static IQueryable<T> FilterBy<T>(this IQueryable<T> query, int? filterInteger,
Expression<Func<T, int?>> memberExpression)
{
if (filterInteger == null)
return query;
var valueExpression = Expression.Constant(filterInteger);
var call = Expression.Equal(memberExpression.Body, valueExpression);
var sourceParam = memberExpression.Parameters.First();
Expression<Func<T, bool>> predicate = Expression.Lambda<Func<T, bool>>(call, sourceParam);
return query.Where(predicate);
}
Boolean
public static IQueryable<T> FilterBy<T>(this IQueryable<T> query, bool? filterBoolean,
Expression<Func<T, bool?>> memberExpression)
{
if (filterBoolean == null)
return query;
var valueExpression = Expression.Constant(filterBoolean);
var call = Expression.Equal(memberExpression.Body, valueExpression);
var sourceParam = memberExpression.Parameters.First();
Expression<Func<T, bool>> predicate = Expression.Lambda<Func<T, bool>>(call, sourceParam);
return query.Where(predicate);
}

I've not tested this but I believe you'd need to use expressions to achieve this. The following will build an expression to use as the predicate in the Where method:
public static IQueryable<T> FilterBy<T>(
this IQueryable<T> query,
string searchValue,
Expression<Func<T, string>> memberExpression)
{
if (string.IsNullOrWhiteSpace(searchValue))
return query;
// must be a lambda expression
LambdaExpression lambdaExpression = memberExpression as LambdaExpression;
if (lambdaExpression == null)
throw new ArgumentException($"Expression '{memberExpression}' is not a lambda expression.");
// get the member
Func<ParameterExpression, Expression> sourceExpression = source => Expression.Invoke(lambdaExpression, source);
ParameterExpression sourceParameter = Expression.Parameter(typeof(T), "source");
Expression sourceMember = sourceExpression(sourceParameter);
// expression for the search value
ConstantExpression valueExpression = Expression.Constant(searchValue);
// expression to call the Contains method
MethodInfo containsMethod = GetContainsMethod();
MethodCallExpression callExpression = Expression.Call(null, containsMethod, sourceMember, valueExpression);
// predicate expression
Expression<Func<T, bool>> predicate = Expression.Lambda<Func<T, bool>>(callExpression, sourceParameter);
return query.Where(predicate);
}
private static MethodInfo GetContainsMethod()
{
// get method
MethodInfo genericContainsMethod = typeof(Queryable)
.GetMethods(BindingFlags.Static | BindingFlags.Public)
.First(m => m.Name == "Contains"
&& m.IsGenericMethod
&& m.GetParameters().Count() == 2);
// apply generic types
MethodInfo containsMethod = genericContainsMethod
.MakeGenericMethod(new Type[] { typeof(string) });
return containsMethod;
}

How to pass a lambda expression to a method expecting lambda expression?

I have an extension method to get a property name as string:
public static string GetPropertyName<T, TResult>(this T obj, Expression<Func<T, TResult>> propertyId)
{
return ((MemberExpression)propertyId.Body).Member.Name;
}
Now I have another method, expecting to pass in list (param) of this kind of property lamba expression.
I want this new method to reuse the 1st method, but can't figure out how to pass it over
public string Test<T>(params Expression<Func<T, object>>[] ps)
{
foreach (var p in ps)
{
var howToCodeThis = p.GetPropertyName(dummy => dummy);
expected usage:
var result = Test<Something>(request.Sorting
, x => x.prop1
, x => x.prop2
, x => x.prop3
);
Update:
Backs answer worked once I change my GetPropertyName to cater for UnaryExpression:
public static string GetPropertyName<T, TResult>(this T obj, Expression<Func<T, TResult>> propertyId)
{
if (propertyId.Body is MemberExpression)
return ((MemberExpression)propertyId.Body).Member.Name;
if (propertyId.Body is UnaryExpression)
{
var op = ((UnaryExpression)propertyId.Body).Operand;
return ((MemberExpression)op).Member.Name;
}
throw new NotImplementedException(string.Format("GetPropertyName - {0}", propertyId.Body.GetType().FullName));
}

var howToCodeThis = GetPropertyName(default(T), p);
OR
var howToCodeThis = default(T).GetPropertyName(p);
But I noteced, you don't use obj in GetPropertyName method.

Trouble with building a C# EntityFramework IQueryable Expression

So I'm attempting to build a semi complication Search expression, but I'm stuck trying to create a basic one. The expressions being used for getValueExpression look something like:
x => x.PropertyA != null ? x.PropertyA.ToShortDateString() : "" //nullable datetime
x => x.PropertyB //string property
x => x.PropertyC != null x.PropertyC.ToString() : "" //nullable int
Here is my function code, it currently errors when getValueExpression being of type Func that can't be compared to a string, which makes perfect sense and I understand why that is, but I'm having trouble figuring out how to make an expression that gets the value of getValueExpression to compare to the value being searched for. Any help or leads in the right direction would be greatly appreciated.
public static IQueryable<TSource> Search<TSource>(this IQueryable<TSource> source, Expression<Func<TSource, string>> getValueExpression, string searchOption, string searchValue)
{
var searchValueExpression = Expression.Constant(searchValue);
var comparisonExpression = Expression.Equal(getValueExpression, searchValueExpression);
var lambdaExpression = Expression.Lambda<Func<TSource, bool>>(comparisonExpression);
return source.Where(lambdaExpression);
}
I've attempted similar things like this, but have met failure with incorrect arguments amount exception:
var getValueExpressionValue = Expression.Call(getValueExpression.Compile().Method, parameterValueExpression);

Here is a method that will let you compose expressions; that is to say you can use the output of one expression as the input of another, creating a new expression taking the input that the first takes and the output that the second takes:
public static Expression<Func<TFirstParam, TResult>>
Compose<TFirstParam, TIntermediate, TResult>(
this Expression<Func<TFirstParam, TIntermediate>> first,
Expression<Func<TIntermediate, TResult>> second)
{
var param = Expression.Parameter(typeof(TFirstParam), "param");
var newFirst = first.Body.Replace(first.Parameters[0], param);
var newSecond = second.Body.Replace(second.Parameters[0], newFirst);
return Expression.Lambda<Func<TFirstParam, TResult>>(newSecond, param);
}
Which uses the following method to replace one expression with another:
internal class ReplaceVisitor : ExpressionVisitor
{
private readonly Expression from, to;
public ReplaceVisitor(Expression from, Expression to)
{
this.from = from;
this.to = to;
}
public override Expression Visit(Expression node)
{
return node == from ? to : base.Visit(node);
}
}
public static Expression Replace(this Expression expression,
Expression searchEx, Expression replaceEx)
{
return new ReplaceVisitor(searchEx, replaceEx).Visit(expression);
}
This lets you write:
public static IQueryable<TSource> Search<TSource>(this IQueryable<TSource> source,
Expression<Func<TSource, string>> getValueExpression,
string searchOption,
string searchValue)
{
var predicate = getValueExpression.Compose(value => value == searchValue);
return source.Where(predicate);
}

Here is how you can do it :
public static IQueryable<TSource> Search<TSource>(this IQueryable<TSource> source, Expression<Func<TSource, string>> getValueExpression, string searchOption, string searchValue)
{
// const searchValue
var searchValueExpression = Expression.Constant(searchValue);
// parameter x
var parameterExpression = Expression.Parameter(typeof(TSource));
// func(x)
var parameterGetValueExpression = Expression.Invoke(getValueExpression, parameterExpression);
// func(x) == searchValue
var comparisonExpression = Expression.Equal(parameterGetValueExpression, searchValueExpression);
// x => func(x) == searchValue
var lambdaExpression = Expression.Lambda<Func<TSource, bool>>(comparisonExpression, parameterExpression);
return source.Where(lambdaExpression);
}

Generic Linq to Entities filter method that accepts filter criteria and properties to be filtered

I've looked into many generic linq filtering questions and their answers here in SO but none of them satisfy my needs so I thought I should create a question.
I've created many of what I call "filter provider" classes, one for each entity class in my model, to provide a simplistic search for my application. I didn't want to go into more advanced solutions like Lucene.Net because a basic filtering with matching score would suffice.
Inside each one of these provider classes there are multiple methods that will receive the filtering terms and query specific properties, returning a score for each match based on the relevance of the property. Most methods will filter multiple properties at once, but not all.
Here are two of these methods:
private IQueryable<Retailer> MatchHighRelevanceFields(string searchTerm, IQueryable<Retailer> retailers)
{
var results = retailers.Where(r =>
(r.CompanyName != null && r.CompanyName.ToUpper().Contains(searchTerm))
|| (r.TradingName != null && r.TradingName.ToUpper().Contains(searchTerm))
);
return results;
}
private IQueryable<Retailer> MatchMediumRelevanceFields(string searchTerm, IQueryable<Retailer> retailers)
{
var results = retailers.Where(r =>
(r.Address.Street != null && r.Address.Street.ToUpper().Contains(searchTerm))
|| (r.Address.Complement != null && r.Address.Complement.ToUpper().Contains(searchTerm))
);
return results;
}
These methods are replicated ad nauseum throughout each provider class and I hope I could replace them for a single method that would receive the properties to be included in the query.
Something like:
public static IQueryable<T> Match<T>(string searchTerm, IQueryable<T> data, Expression<Func<T, string>> filterProperties)
{
var results = **build the query for each property in filterProperties**
return results;
}
But I really can't figure it out. I tried using reflection but it only worked with Linq to Objects and I need a solution for Linq to Entities.

So to solve this problem we need a few puzzle pieces first. The first puzzle piece is a method that can take an expression that computes a value, and then another expression that computes a new value taking the same type the first returns, and creates a new expression that represents the result of passing the result of the first function as the parameter to the second. This allows us to Compose expressions:
public static Expression<Func<TFirstParam, TResult>>
Compose<TFirstParam, TIntermediate, TResult>(
this Expression<Func<TFirstParam, TIntermediate>> first,
Expression<Func<TIntermediate, TResult>> second)
{
var param = Expression.Parameter(typeof(TFirstParam), "param");
var newFirst = first.Body.Replace(first.Parameters[0], param);
var newSecond = second.Body.Replace(second.Parameters[0], newFirst);
return Expression.Lambda<Func<TFirstParam, TResult>>(newSecond, param);
}
This relies on the following tool to replace all instances of one expression with another:
public static Expression Replace(this Expression expression,
Expression searchEx, Expression replaceEx)
{
return new ReplaceVisitor(searchEx, replaceEx).Visit(expression);
}
internal class ReplaceVisitor : ExpressionVisitor
{
private readonly Expression from, to;
public ReplaceVisitor(Expression from, Expression to)
{
this.from = from;
this.to = to;
}
public override Expression Visit(Expression node)
{
return node == from ? to : base.Visit(node);
}
}
We'll also need a tool to help us OR two predicate expressions together:
public static class PredicateBuilder
{
public static Expression<Func<T, bool>> True<T>() { return f => true; }
public static Expression<Func<T, bool>> False<T>() { return f => false; }
public static Expression<Func<T, bool>> Or<T>(
this Expression<Func<T, bool>> expr1,
Expression<Func<T, bool>> expr2)
{
var secondBody = expr2.Body.Replace(
expr2.Parameters[0], expr1.Parameters[0]);
return Expression.Lambda<Func<T, bool>>
(Expression.OrElse(expr1.Body, secondBody), expr1.Parameters);
}
public static Expression<Func<T, bool>> And<T>(
this Expression<Func<T, bool>> expr1,
Expression<Func<T, bool>> expr2)
{
var secondBody = expr2.Body.Replace(
expr2.Parameters[0], expr1.Parameters[0]);
return Expression.Lambda<Func<T, bool>>
(Expression.AndAlso(expr1.Body, secondBody), expr1.Parameters);
}
}
Now that we have this we can use Compose on each property selector to map it from the property results to whether or not that property value is non-null and contains the search term. We can then OR all of those predicates together to get a filter for your query:
public static IQueryable<T> Match<T>(
IQueryable<T> data,
string searchTerm,
IEnumerable<Expression<Func<T, string>>> filterProperties)
{
var predicates = filterProperties.Select(selector =>
selector.Compose(value =>
value != null && value.Contains(searchTerm)));
var filter = predicates.Aggregate(
PredicateBuilder.False<T>(),
(aggregate, next) => aggregate.Or(next));
return data.Where(filter);
}

You can do it with expression trees but it's not as simple as you might think.
public static IQueryable<T> Match<T>(this IQueryable<T> data, string searchTerm,
params Expression<Func<T, string>>[] filterProperties)
{
var parameter = Expression.Parameter(typeof (T), "source");
Expression body = null;
foreach (var prop in filterProperties)
{
// need to replace all the expressions with the one parameter (gist taken from Colin Meek blog see link on top of class)
//prop.body should be the member expression
var propValue =
prop.Body.ReplaceParameters(new Dictionary<ParameterExpression, ParameterExpression>()
{
{prop.Parameters[0], parameter}
});
// is null check
var isNull = Expression.NotEqual(propValue, Expression.Constant(null, typeof(string)));
// create a tuple so EF will parameterize the sql call
var searchTuple = Tuple.Create(searchTerm);
var matchTerm = Expression.Property(Expression.Constant(searchTuple), "Item1");
// call ToUpper
var toUpper = Expression.Call(propValue, "ToUpper", null);
// Call contains on the ToUpper
var contains = Expression.Call(toUpper, "Contains", null, matchTerm);
// And not null and contains
var and = Expression.AndAlso(isNull, contains);
// or in any additional properties
body = body == null ? and : Expression.OrElse(body, and);
}
if (body != null)
{
var where = Expression.Call(typeof (Queryable), "Where", new[] {typeof (T)}, data.Expression,
Expression.Lambda<Func<T, bool>>(body, parameter));
return data.Provider.CreateQuery<T>(where);
}
return data;
}
public static Expression ReplaceParameters(this Expression exp, IDictionary<ParameterExpression, ParameterExpression> map)
{
return new ParameterRebinder(map).Visit(exp);
}
Now you need to have a expressionvisitor to make all the expressions use one parameter
//http://blogs.msdn.com/b/meek/archive/2008/05/02/linq-to-entities-combining-predicates.aspx
public class ParameterRebinder : ExpressionVisitor
{
private readonly IDictionary<ParameterExpression, ParameterExpression> _map;
public ParameterRebinder(IDictionary<ParameterExpression, ParameterExpression> map)
{
_map = map;
}
protected override Expression VisitParameter(ParameterExpression node)
{
if (_map.ContainsKey(node))
{
return _map[node];
}
return base.VisitParameter(node);
}
}
Would use it like
var matches = retailers.Match("7", r => r.Address.Street, x => x.Address.Complement).ToList();
Warning - I checked this with linq to objects using the AsQueryable but didn't run it against EF.

You can use Linq.Dynamic to build the query.
public static IQueryable<T> Match<T>(
string searchTerm,
IQueryable<T> data,
params Expression<Func<T, string>>[] filterProperties) where T : class
{
var predicates = new List<string>();
foreach (var prop in filterProperties)
{
var lambda = prop.ToString();
var columnName = lambda.Substring(lambda.IndexOf('.') + 1);
var predicate = string.Format(
"({0} != null && {0}.ToUpper().Contains(#0))", columnName);
predicates.Add(predicate);
}
var filter = string.Join("||", predicates);
var results = data.Where(filter, searchTerm);
return results;
}
Usage.
var retailers = Match(
"asd", db.Retailers, r => r.CompanyName, r => r.TradingName);
var retailers = Match(
"asd", db.Retailers, r => r.Address.Street, r => r.Address.Complement);
Limitation.
The filter can only accept basic expression.
r => r.Name
r => r.PropA.Name
r => r.PropA.PropB.Name

Try to use Expressions like those all
http://www.codeproject.com/Articles/493917/Dynamic-Querying-with-LINQ-to-Entities-and-Express

Unbind parameter

all
I try to build a dynamic linq query by expression tree, below is my code
Expression<Func<User, bool>> filter = c => c.isAdmin == false;
Expression<Func<User, bool>> filterForExistUser = c => (c.isfreezed == null ? false : c.isfreezed) != true;
Expression<Func<User, bool>> finalFilter = Expression.Lambda<Func<User, bool>>(Expression.AndAlso(filter.Body, filterForExistUser.Body), filter.Parameters);
IQueryable<User> myusers = db.Users.AsQueryable<User>();
MethodCallExpression whereCallExpression = Expression.Call(
typeof(Queryable),
"Where",
new Type[] { myusers.ElementType },
myusers.Expression,
finalFilter);
IQueryable<User> results = myusers.Provider.CreateQuery<User>(whereCallExpression);
foreach (User user in results)
Console.WriteLine(user.UserName);
But system report "unding parameter c" error, how I can fix it?
Thanks

Although the parameters in the filter and filterForExistUser expressions share the same name, they both are referring to different symbols from different scopes. Your new expression uses the parameter from the filter expression, but you left out the parameter for the filterForExistUser. You must rewrite the expression so the same single parameter is used throughout the overall expression.
Here's a general purpose method you can use to combine the predicates:
Expression<Func<TSource, bool>> CombinePredicates<TSource>(
Expression<Func<TSource, bool>> head,
params Expression<Func<TSource, bool>>[] tail)
{
var param = head.Parameters.Single();
var body = tail.Aggregate(
head.Body,
(result, expr) => Expression.AndAlso(result,
new SubstitutionVisitor
{
OldExpr = expr.Parameters.Single(),
NewExpr = param,
}.Visit(expr.Body)
)
);
return Expression.Lambda<Func<TSource, bool>>(body, param);
}
public class SubstitutionVisitor : ExpressionVisitor
{
public Expression OldExpr { get; set; }
public Expression NewExpr { get; set; }
public override Expression Visit(Expression node)
{
return (node == OldExpr) ? NewExpr : base.Visit(node);
}
}
The key is the SubstitutionVisitor which is used to substitute the "tail" paramters using the "head" parameter.
So your final filter becomes this:
Expression<Func<User, bool>> finalFilter =
CombinePredicates(filter, filterForExistUser);