Here's what the required function would look like:
public static Expression<Func<T, T>> GetExpression<T>(string propertyNames) where T : class
{
var properties = propertyNames.Split(
new char[] { ',' },
StringSplitOptions.RemoveEmptyEntries
).ToList();
//need help here
}
Currently I'm doing it like this:
_context.Questions.Select(q =>
new Question() {
QuestionId = q.QuestionId,
QuestionEnglish = q.QuestionEnglish
}
).ToList();
And I want to replace it with:
_context.Questions.Select(GetExpression<Question>("QuestionId, QuestionInEnglish")).ToList();
Any help would be greatly appreciated.
You can do it like this;
public static Func<T, T> GetExpression<T>(string propertyNames)
{
var xParameter = Expression.Parameter(typeof(T), "parameter");
var xNew = Expression.New(typeof(T));
var selectFields = propertyNames.Split(',').Select(parameter => parameter.Trim())
.Select(parameter => {
var prop = typeof(T).GetProperty(parameter);
if (prop == null) // The field doesn't exist
{
return null;
}
var xOriginal = Expression.Property(xParameter, prop);
return Expression.Bind(prop, xOriginal);
}
).Where(x => x != null);
var lambda = Expression.Lambda<Func<T, T>>(Expression.MemberInit(xNew, selectFields), xParameter);
return lambda.Compile();
}
Usage;
var list = new List<Question>{new Question{QuestionEnglish = "QuestionName",QuestionId = 1}};
var result = list.Select(GetExpression<Question>("QuestionId, QuestionEnglish"));
Please how do we construct a dynamic where filter in EF.Core to handle:
Query.Where(fieldName, compareMode, value)
I basically Expect to use it like below:
[HttpGet(Name = nameof(GetStaff))]
public IActionResult GetStaffAsync([FromQuery] QueryParams p)
{
var s = db.Staff.AsNoTracking()
.Where(p.filter_field, p.filter_mode, p.filter_value)
.OrderByMember(p.sortBy, p.descending);
var l = new Pager<Staff>(s, p.page, p.rowsPerPage);
return Ok(l);
}
//Helpers
public class QueryParams
{
public bool descending { get; set; }
public int page { get; set; } = 1;
public int rowsPerPage { get; set; } = 5;
public string sortBy { get; set; }
public onject filter_value { get; set; }
public string filter_field { get; set; }
public string filter_mode { get; set; }
}
public class Pager<T>
{
public int pages { get; set; }
public int total { get; set; }
public IEnumerable<T> Items { get; set; }
public Pager(IEnumerable<T> items, int offset, int limit)
{
Items = items.Skip((offset - 1) * limit).Take(limit).ToList<T>();
total = items.Count();
pages = (int)Math.Ceiling((double)total / limit);
}
}
Assuming all you have is the entity type and strings representing the property, comparison operator and the value, building dynamic predicate can be done with something like this:
public static partial class ExpressionUtils
{
public static Expression<Func<T, bool>> BuildPredicate<T>(string propertyName, string comparison, string value)
{
var parameter = Expression.Parameter(typeof(T), "x");
var left = propertyName.Split('.').Aggregate((Expression)parameter, Expression.Property);
var body = MakeComparison(left, comparison, value);
return Expression.Lambda<Func<T, bool>>(body, parameter);
}
private static Expression MakeComparison(Expression left, string comparison, string value)
{
switch (comparison)
{
case "==":
return MakeBinary(ExpressionType.Equal, left, value);
case "!=":
return MakeBinary(ExpressionType.NotEqual, left, value);
case ">":
return MakeBinary(ExpressionType.GreaterThan, left, value);
case ">=":
return MakeBinary(ExpressionType.GreaterThanOrEqual, left, value);
case "<":
return MakeBinary(ExpressionType.LessThan, left, value);
case "<=":
return MakeBinary(ExpressionType.LessThanOrEqual, left, value);
case "Contains":
case "StartsWith":
case "EndsWith":
return Expression.Call(MakeString(left), comparison, Type.EmptyTypes, Expression.Constant(value, typeof(string)));
default:
throw new NotSupportedException($"Invalid comparison operator '{comparison}'.");
}
}
private static Expression MakeString(Expression source)
{
return source.Type == typeof(string) ? source : Expression.Call(source, "ToString", Type.EmptyTypes);
}
private static Expression MakeBinary(ExpressionType type, Expression left, string value)
{
object typedValue = value;
if (left.Type != typeof(string))
{
if (string.IsNullOrEmpty(value))
{
typedValue = null;
if (Nullable.GetUnderlyingType(left.Type) == null)
left = Expression.Convert(left, typeof(Nullable<>).MakeGenericType(left.Type));
}
else
{
var valueType = Nullable.GetUnderlyingType(left.Type) ?? left.Type;
typedValue = valueType.IsEnum ? Enum.Parse(valueType, value) :
valueType == typeof(Guid) ? Guid.Parse(value) :
Convert.ChangeType(value, valueType);
}
}
var right = Expression.Constant(typedValue, left.Type);
return Expression.MakeBinary(type, left, right);
}
}
Basically building property accessor (with nested property support), parsing the comparison operator and calling the corresponding operator/method, dealing with from/to string and from/to nullable type conversions. It can be extended to handle EF Core specific functions like EF.Functions.Like by adding the corresponding branch.
It can be used directly (in case you need to combine it with other predicates) or via custom extension method like this:
public static partial class QueryableExtensions
{
public static IQueryable<T> Where<T>(this IQueryable<T> source, string propertyName, string comparison, string value)
{
return source.Where(ExpressionUtils.BuildPredicate<T>(propertyName, comparison, value));
}
}
based on Ivans answer this is what i came up with
public static class ExpressionUtils
{
public static Expression<Func<T, bool>> BuildPredicate<T>(string propertyName, string comparison, object value)
{
var parameter = Expression.Parameter(typeof(T));
var left = propertyName.Split('.').Aggregate((Expression)parameter, Expression.PropertyOrField);
var body = MakeComparison(left, comparison, value);
return Expression.Lambda<Func<T, bool>>(body, parameter);
}
static Expression MakeComparison(Expression left, string comparison, object value)
{
var constant = Expression.Constant(value, left.Type);
switch (comparison)
{
case "==":
return Expression.MakeBinary(ExpressionType.Equal, left, constant);
case "!=":
return Expression.MakeBinary(ExpressionType.NotEqual, left, constant);
case ">":
return Expression.MakeBinary(ExpressionType.GreaterThan, left, constant);
case ">=":
return Expression.MakeBinary(ExpressionType.GreaterThanOrEqual, left, constant);
case "<":
return Expression.MakeBinary(ExpressionType.LessThan, left, constant);
case "<=":
return Expression.MakeBinary(ExpressionType.LessThanOrEqual, left, constant);
case "Contains":
case "StartsWith":
case "EndsWith":
if (value is string)
{
return Expression.Call(left, comparison, Type.EmptyTypes, constant);
}
throw new NotSupportedException($"Comparison operator '{comparison}' only supported on string.");
default:
throw new NotSupportedException($"Invalid comparison operator '{comparison}'.");
}
}
}
and some tests
public class Tests
{
[Fact]
public void Nested()
{
var list = new List<Target>
{
new Target
{
Member = "a"
},
new Target
{
Member = "bb"
}
};
var result = list.AsQueryable()
.Where(ExpressionUtils.BuildPredicate<Target>("Member.Length", "==", 2))
.Single();
Assert.Equal("bb", result.Member);
}
[Fact]
public void Field()
{
var list = new List<TargetWithField>
{
new TargetWithField
{
Field = "Target1"
},
new TargetWithField
{
Field = "Target2"
}
};
var result = list.AsQueryable()
.Where(ExpressionUtils.BuildPredicate<TargetWithField>("Field", "==", "Target2"))
.Single();
Assert.Equal("Target2", result.Field);
}
[Theory]
[InlineData("Name", "==", "Person 1", "Person 1")]
[InlineData("Name", "!=", "Person 2", "Person 1")]
[InlineData("Name", "Contains", "son 2", "Person 2")]
[InlineData("Name", "StartsWith", "Person 2", "Person 2")]
[InlineData("Name", "EndsWith", "son 2", "Person 2")]
[InlineData("Age", "==", 13, "Person 2")]
[InlineData("Age", ">", 12, "Person 2")]
[InlineData("Age", "!=", 12, "Person 2")]
[InlineData("Age", ">=", 13, "Person 2")]
[InlineData("Age", "<", 13, "Person 1")]
[InlineData("Age", "<=", 12, "Person 1")]
public void Combos(string name, string expression, object value, string expectedName)
{
var people = new List<Person>
{
new Person
{
Name = "Person 1",
Age = 12
},
new Person
{
Name = "Person 2",
Age = 13
}
};
var result = people.AsQueryable()
.Where(ExpressionUtils.BuildPredicate<Person>(name, expression, value))
.Single();
Assert.Equal(expectedName, result.Name);
}
}
I modified the answer I found here: Linq WHERE EF.Functions.Like - Why direct properties work and reflection does not?
I chucked together a version for those using NpgSQL as their EF Core provider as you will need to use the ILike function instead if you want case-insensitivity, also added a second version which combines a bunch of properties into a single Where() clause:
public static IQueryable<T> WhereLike<T>(this IQueryable<T> source, string propertyName, string searchTerm)
{
// Check property name
if (string.IsNullOrEmpty(propertyName))
{
throw new ArgumentNullException(nameof(propertyName));
}
// Check the search term
if(string.IsNullOrEmpty(searchTerm))
{
throw new ArgumentNullException(nameof(searchTerm));
}
// Check the property exists
var property = typeof(T).GetProperty(propertyName);
if (property == null)
{
throw new ArgumentException($"The property {typeof(T)}.{propertyName} was not found.", nameof(propertyName));
}
// Check the property type
if(property.PropertyType != typeof(string))
{
throw new ArgumentException($"The specified property must be of type {typeof(string)}.", nameof(propertyName));
}
// Get expression constants
var searchPattern = "%" + searchTerm + "%";
var itemParameter = Expression.Parameter(typeof(T), "item");
var functions = Expression.Property(null, typeof(EF).GetProperty(nameof(EF.Functions)));
var likeFunction = typeof(NpgsqlDbFunctionsExtensions).GetMethod(nameof(NpgsqlDbFunctionsExtensions.ILike), new Type[] { functions.Type, typeof(string), typeof(string) });
// Build the property expression and return it
Expression selectorExpression = Expression.Property(itemParameter, property.Name);
selectorExpression = Expression.Call(null, likeFunction, functions, selectorExpression, Expression.Constant(searchPattern));
return source.Where(Expression.Lambda<Func<T, bool>>(selectorExpression, itemParameter));
}
public static IQueryable<T> WhereLike<T>(this IQueryable<T> source, IEnumerable<string> propertyNames, string searchTerm)
{
// Check property name
if (!(propertyNames?.Any() ?? false))
{
throw new ArgumentNullException(nameof(propertyNames));
}
// Check the search term
if (string.IsNullOrEmpty(searchTerm))
{
throw new ArgumentNullException(nameof(searchTerm));
}
// Check the property exists
var properties = propertyNames.Select(p => typeof(T).GetProperty(p)).AsEnumerable();
if (properties.Any(p => p == null))
{
throw new ArgumentException($"One or more specified properties was not found on type {typeof(T)}: {string.Join(",", properties.Where(p => p == null).Select((p, i) => propertyNames.ElementAt(i)))}.", nameof(propertyNames));
}
// Check the property type
if (properties.Any(p => p.PropertyType != typeof(string)))
{
throw new ArgumentException($"The specified properties must be of type {typeof(string)}: {string.Join(",", properties.Where(p => p.PropertyType != typeof(string)).Select(p => p.Name))}.", nameof(propertyNames));
}
// Get the expression constants
var searchPattern = "%" + searchTerm + "%";
var itemParameter = Expression.Parameter(typeof(T), "item");
var functions = Expression.Property(null, typeof(EF).GetProperty(nameof(EF.Functions)));
var likeFunction = typeof(NpgsqlDbFunctionsExtensions).GetMethod(nameof(NpgsqlDbFunctionsExtensions.ILike), new Type[] { functions.Type, typeof(string), typeof(string) });
// Build the expression and return it
Expression selectorExpression = null;
foreach (var property in properties)
{
var previousSelectorExpression = selectorExpression;
selectorExpression = Expression.Property(itemParameter, property.Name);
selectorExpression = Expression.Call(null, likeFunction, functions, selectorExpression, Expression.Constant(searchPattern));
if(previousSelectorExpression != null)
{
selectorExpression = Expression.Or(previousSelectorExpression, selectorExpression);
}
}
return source.Where(Expression.Lambda<Func<T, bool>>(selectorExpression, itemParameter));
}
In a AIR Mobile application I have this code:
import character.*;
var player_1 = new characterObject("Player 1");
var player_2 = new characterObject("Player 2");
In the package class:
package character {
public class characterObject extends MovieClip {
public var characterName: Number;
public var playerCounter: Number = 0;
public function characterObject(myName: String) {
characterName = myName;
playerCounter++;
}
}
Can I access to player_1.playerCounter property inside player_2 object istance?
I need to increes the value of players only if total_player (a var that I want create as sum of player_1.playerCounter + player_2.playerCounter + player_n.playerCounter ...) is < of x.
Bad idea.
Yo can try next thing
package character {
public class CharactersModel extends Object{
private var _chars : Array = [];
public function addCharacter(char : characterObject) {
_chars.push(char);
}
public function getChars() : Array {
return _chars;
}
public function getCharByName(name : String ) : characterObject {
//select from array and return
//use it instead of null
return null;
}
}
}
and update characterObject like this
private var _model : CharactersModel;
public function characterObject(model : CharactersModel ,myName: String) {
_model = model;
characterName = myName;
playerCounter++;
model.addCharacter(this);
}
public function getOtherChar(name : String) {
return _model.getCharByName(name);
}
and finally
import character.*;
var model : CharactersModel = new CharactersModel();
var player_1 = new characterObject(model ,"Player 1");
var player_2 = new characterObject(model ,"Player 2");
I would create a vector to hold character instances outside of the characterObject class. Then you could refer to the length of the vector for the current amount.
var characters:Vector.<characterObject> = new Vector.<characterObject>();
characters.push( new characterObject("Player 1") );
characters.push( new characterObject("Player 2") );
trace( characters.length ); // 2
If I have a doc which has an array which contains a items which represents counts for a day, perhaps like :-
{
data : [ {'20141102' : 2 },{'20141103' : 4 } ]
}
when I do an update, and I have a string '20141103' and then later a '20141104' I want to either inc the array entry or add a new array entry. Is this possible with an update?
Yes, it's feasible. I tried like this:
(run on mongo shell; both client and server are V2.6.4)
function tryAndFine(coll, key, value) {
var entry = {};
entry[key] = value;
var parent = 'data';
var prefix = parent + '.';
function incrementOnly() {
var criteria = {};
criteria[prefix + key] = {$exists : true};
var update = {};
update[prefix + "$." + key] = value;
var result = coll.update(criteria, {$inc : update});
// if increment fails, try to add a new one
if (result.nModified == 0) {
addNewElement();
}
}
function addNewElement() {
var criteria = {};
criteria[prefix + key] = {$exists : false};
var update = {};
update[parent] = entry;
var result = coll.update(criteria, {$push : update}, {upsert : true});
// if exists, try to increment the count
if (result.upserted == 0 && result.nModified == 0) {
incrementOnly();
}
}
// run entry
incrementOnly();
}
// test
var c = db.c;
c.drop();
tryAndFine(c, '20141103', 1);
tryAndFine(c, '20141103', 1);
tryAndFine(c, '20141104', 1);
tryAndFine(c, '20141105', 1);
tryAndFine(c, '20141104', 1);
// output
{
"_id" : ObjectId("54577e1a3502852bd4ad2395"),
"data" : [ {
"20141103" : 2
}, {
"20141104" : 2
}, {
"20141105" : 1
} ]
}
I've Been Trying to change the order of nodes through quickfix, but something is wrong.
Here's my code in xtend:
#Fix(org.xtext.custom.conventions.validation.ConventionsValidator::CONVENTION_NOT_ORDERED)
def fixFeatureName( Issue issue, IssueResolutionAcceptor acceptor){
acceptor.accept(issue, 'Sort', "Sort '" + issue.data.head + "'", null)[
element, context |
var gr=(element as Greeting)
if (gr.name === null || gr.name.length === 0)
return;
var econt=gr.eContainer.eContents
var comparator = [ EObject obj1, EObject obj2 |
var o1 = (obj1 as Greeting)
var o2 = (obj2 as Greeting)
return o1.name.compareTo(o2.name)
]
ECollections::sort(econt, comparator)
]
}
No exception is being thrown to console, in debug I found an UnsupportedOperationException is thrown and handled by xtext.
I suspect that EList is immutable.
So how can I sort the AST?
(Here is the generated code: )
#Fix(ConventionsValidator.CONVENTION_NOT_ORDERED)
public void fixFeatureName(final Issue issue, final IssueResolutionAcceptor acceptor) {
String[] _data = issue.getData();
String _head = IterableExtensions.<String>head(((Iterable<String>)Conversions.doWrapArray(_data)));
String _plus = ("Sort \'" + _head);
String _plus_1 = (_plus + "\'");
final ISemanticModification _function = new ISemanticModification() {
public void apply(final EObject element, final IModificationContext context) throws Exception {
Greeting gr = ((Greeting) element);
boolean _or = false;
String _name = gr.getName();
boolean _tripleEquals = (_name == null);
if (_tripleEquals) {
_or = true;
} else {
String _name_1 = gr.getName();
int _length = _name_1.length();
boolean _tripleEquals_1 = (Integer.valueOf(_length) == Integer.valueOf(0));
_or = (_tripleEquals || _tripleEquals_1);
}
if (_or) {
return;
}
EObject _eContainer = gr.eContainer();
EList<EObject> econt = _eContainer.eContents();
final Function2<EObject,EObject,Integer> _function = new Function2<EObject,EObject,Integer>() {
public Integer apply(final EObject obj1, final EObject obj2) {
Greeting o1 = ((Greeting) obj1);
Greeting o2 = ((Greeting) obj2);
String _name = o1.getName();
String _name_1 = o2.getName();
return _name.compareTo(_name_1);
}
};
Function2<EObject,EObject,Integer> comparator = _function;
final Function2<EObject,EObject,Integer> _converted_comparator = (Function2<EObject,EObject,Integer>)comparator;
ECollections.<EObject>sort(econt, new Comparator<EObject>() {
public int compare(EObject o1,EObject o2) {
return _converted_comparator.apply(o1,o2);
}
});
}
};
acceptor.accept(issue, "Sort", _plus_1, null, _function);
}
thanks!
Sorting a temporary collection which will then replace econt didn't work. but I managed to solve it in a different way.
so one solution was to force a cast of eContainer as it's runtime element (which is Model), and then getting a list with it's getGreetings getter, and with that element the sorting works, but I didn't want to involve non-generic code, for technical reasons.
So after a lot of experiments I finally found that element without involving any other elements or keywords from the grammar:
var econt = (gr.eContainer.eGet(gr.eContainingFeature) as EObjectContainmentEList<Greeting>)
and that is exactly what was looking for. Sorting is successful!
Here's the resulting Xtend code (got rid of casing in the comperator as well):
#Fix(ConventionsValidator::CONVENTION_NOT_ORDERED)
def fixFeatureName(Issue issue, IssueResolutionAcceptor acceptor) {
acceptor.accept(issue, 'Sort', "Sort '" + issue.data.head + "'", null) [
element, context |
var gr = (element as Greeting)
if (gr.name === null || gr.name.length === 0)
return;
var econt = (gr.eContainer.eGet(gr.eContainingFeature) as EObjectContainmentEList<Greeting>)
var comparator = [ Greeting o1, Greeting o2 |
return o1.name.compareTo(o2.name)
]
ECollections::sort(econt, comparator)
]
}
and the generated java:
#Fix(ConventionsValidator.CONVENTION_NOT_ORDERED)
public void fixFeatureName(final Issue issue, final IssueResolutionAcceptor acceptor) {
String[] _data = issue.getData();
String _head = IterableExtensions.<String>head(((Iterable<String>)Conversions.doWrapArray(_data)));
String _plus = ("Sort \'" + _head);
String _plus_1 = (_plus + "\'");
final ISemanticModification _function = new ISemanticModification() {
public void apply(final EObject element, final IModificationContext context) throws Exception {
Greeting gr = ((Greeting) element);
boolean _or = false;
String _name = gr.getName();
boolean _tripleEquals = (_name == null);
if (_tripleEquals) {
_or = true;
} else {
String _name_1 = gr.getName();
int _length = _name_1.length();
boolean _tripleEquals_1 = (Integer.valueOf(_length) == Integer.valueOf(0));
_or = (_tripleEquals || _tripleEquals_1);
}
if (_or) {
return;
}
EObject _eContainer = gr.eContainer();
EStructuralFeature _eContainingFeature = gr.eContainingFeature();
Object _eGet = _eContainer.eGet(_eContainingFeature);
EObjectContainmentEList<Greeting> econt = ((EObjectContainmentEList<Greeting>) _eGet);
final Function2<Greeting,Greeting,Integer> _function = new Function2<Greeting,Greeting,Integer>() {
public Integer apply(final Greeting o1, final Greeting o2) {
String _name = o1.getName();
String _name_1 = o2.getName();
return _name.compareTo(_name_1);
}
};
Function2<Greeting,Greeting,Integer> comparator = _function;
final Function2<Greeting,Greeting,Integer> _converted_comparator = (Function2<Greeting,Greeting,Integer>)comparator;
ECollections.<Greeting>sort(econt, new Comparator<Greeting>() {
public int compare(Greeting o1,Greeting o2) {
return _converted_comparator.apply(o1,o2);
}
});
}
};
acceptor.accept(issue, "Sort", _plus_1, null, _function);
}