Oasis.DynamicFilter (referred to as the library in the following content) is a library that helps users (referred to as "developers" in the following document, as users of this libraries are developers) to automatically generate a linq expression/function to filter some class instances according to a filter class. Simply summarizing the feature, it helps to filter instances of one class with another.
During implementation of a web application, searching for data according to certain criteria is a common requirement, that developers provide a searching panel to let business users provide some input values, then the input value gets sent to the server side, and the input values will be used to filter data in the database, at last the filter data will be sent back to web application and response of the search request. For simple searching use cases, the search logic is always simple and similar, yet for every search developers has to repeat the tedious and brainless coding to fill it in. An example of such case is demonstrated as this example. In a library system, each book has a name and published year. To search for the book by either name or published year in the database, the code may be like the following:
// assume Book is already declared in the entity framework database context, and SearchForBookDto is the class that contains the business user input
public class Book
{
public string Name { get; set; } = null!;
public int PublishedYear { get; set; }
}
public class SearchForBookDto
{
public string Name { get; set; } = null!;
public int? PublishedYear { get; set; }
}// searching logis is like this
IQueryable queryable = databaseContext.Set<Book>();
if (searchForBookDto.Name != null)
{
queryable = queryable.Where(book => book.Name == searchForBookDto.Name);
}
if (searchForBookDto.PublishedYear != null)
{
queryable = queryable.Where(book => book.PublishedYear == searchForBookDto.PublishedYear);
}
await queryable.ToListAsync();It's easy to see in the use case that for each searching property, the logic is the same: if the property value is not null, apply it to the queryable. This is quite tedious if there are a lot of such search fields to fill in for, or there are a lot of such searching features to implement. The library helps to implement the same searching logic and simply the code to be as following:
var expressionMaker = new FilterBuilder().Register<Book, SearchForBookDto>().Build();
await databaseContext.Set<Book>().Where(expressionMaker.GetExpression<Book, SearchForBookDto>(searchForBookDto)).ToListAsync();The library uses ILGenerator class provided by C# to dynamically generate the "If not null then apply the search" logic code in IL to save developers the effort. FilterBuilder.Register<TEntity, TFilter> method automatically tries to scan over all public instance properties of the TEntity and TFilter classes, find the property pairs with the same names, detect types of both entity and filter properties, and apply default operation it should use for the filtering. The default filtering operation applied between properties types of certain types are listed below.
| Entity Property Type | Filter Property Type | Default Operation |
|---|---|---|
| C# primitive numeric | C# primitive numeric | Equal |
| string | string | Equal |
| Decimal | Decimal | Equal |
| DateTime | DateTime | Equal |
| other value types (custom enum or struct if equal operator is defined) | same value type | Equal |
| ICollection where T is string or value type | same string or value type | Contains |
| T[] where T is string or value type | same string or value type | Contains |
| some string or value type | ICollection where T is the same string or value type | In |
| some string or value type | T[] where T is the same string or value type | In |
Note that if the property types are not suitable for any operator, the property pair will be silently ignored by the library when filtering. When both etity and property types are string, the default operator is by default Equal, but configurable. This will be elaborated in the later sections. Note that for C# primitive numeric values comparison, the types don't need to be exactly the same, like comparison between an int and a long is allowed, also that between a sbyte and ushort. As long as C# allows the comparison, the library supportes it. But for custom defined enums structs and classes, comparison is only allowed to happen between instances of the same type, for structs and classes, the corresponding compairson operator must exist as well. In the above table, "In" logic represents simply the reverse of contains, that if the string or numeric value is in the collection or array. Developers can call register for multiple times to register filtering relationship between multiple class pairs, when finished call FilterBuilder.Build method to finish it get the IFilter instance that generates expressions. To get a function to filter IEnumerable instances, developers can call IFilter.GetFunction<TEntity, TFilter> instead of calling IFilter.GetExpression<TEntity, TFilter>, or they can simple call Compile method from the expression to get the function, they are essentially the same.
To fit the library with more general use cases, the library allows users to filter with custom configurations. For a more complicated use case to filter books with a partial of author name and author age when the book is published:
public sealed class Book
{
public int PublishedYear { get; set; }
public string Name { get; set; } = null!;
public Author Author { get; set; } = null!;
}
public sealed class Author
{
public int BirthYear { get; set; }
public string Name { get; set; } = null!;
}
public sealed class BookFilter
{
public int? PublishedYear { get; set; } = default!;
public string? Name { get; set; }
}To get all books from an author whose name contains string "John" and whose age is below 40 when the book is published, the following code should get the expression:
var expressionMaker = new FilterBuilder()
.Configure<Book, AuthorFilter>()
.Filter(filter => book => book.Author.Name.Contains(filter.AuthorName!), filter => !string.IsNullOrEmpty(filter.AuthorName))
.Filter(filter => book => book.PublishedYear - book.Author.BirthYear < filter.Age, filter => filter.Age.HasValue)
.Finish()
.Build();
var filter = new AuthorFilter { Age = 40, AuthorName = "John" };
var exp = expressionMaker.GetExpression<Book, AuthorFilter>(filter);For .Filter method, the first parameter is the method to apply filter to entity, in this case the how to use input filter to include/exclude books; the second parameter is a function to decide whether to apply this filter. Take the sample code above, the first .Filter call suggests, that if AuthorName of filter is not an empty string, selected books' author names must contain the value of AuthorName of the filter or else author name of book is not used for filtering; the second .Filter call suggests that if Age of filter has value, selected book must be published before the author became the age, or else books' publish year or author birth year will not be used for fitering the books. The second parameter of .Filter will be null if not passed, which means the filtering condition will be applied regardless of what values the filter has. The filtering conditions in the 2 .Filter calls will be combined with "AndAlso" operator when filtering. Of course we can use a single .Filter call to implement the same behavior, just in that case we'll have to make some adjustment to move the "whether to apply the filter" parameter content to the filter method parameter, because flexibility of whether to apply each filtering method is no longer a possibility with the combination:
var expressionMaker = new FilterBuilder()
.Configure<Book, AuthorFilter>()
.Filter(filter => book => (string.IsNullOrEmpty(filter.AuthorName) || book.Author.Name.Contains(filter.AuthorName)) && (!filter.Age.HasValue || book.PublishedYear - book.Author.BirthYear < filter.Age))
.Finish()
.Build();This feature allows developers to filter entities with more complicated expressions rather than only with existing property values, which adds a lot of flexibility for developers and makes the library way more powerful. Note that to make use of this feature when querying data in database, the expression passed in for entity property must be supported by Linq to SQL.
When building a filtering rule between a filter and entity, with .Configure method, the library will still try to find scan over both classes, and try to generate filtering code for properties of same names and compatible types. If the same property is used in custom configuration and shouldn't be used for automatic filtering, .ExcludeProperties method should be called to stop the library from automatically generating filtering code for that property. Like the case:
public sealed class Book
{
public int Id { get; set; }
public int PublishedYear { get; set; }
public string Name { get; set; } = null!;
public int AuthorId { get; set; }
public Author Author { get; set; } = null!;
}
public sealed class BookByNameFilter
{
public string? Name { get; set; } = null!;
}If we want to use the filter to find books whose name contains the value of filter, like book name is "Book 1", and we pass "k 1" to BookByNameFilter.Name and hoping to use it to find "Book 1" because string "Book 1" contains string "k 1", the code below is the correct configuration.
var expressionMaker = new FilterBuilder()
.Configure<Book, BookByNameFilter>()
.ExcludeProperties(book => book.Name)
.Filter(filter => book => book.Name.Contains(filter.Name!), filter => !string.IsNullOrEmpty(filter.Name))
.Finish()
.Build();Note that without the statement ".ExcludeProperties(book => book.Name)", the library will automatically generate the condition that book name should equal to book filter name, so the final condition becomes "book names equals to book filter name, and book name contains book filter name", which will only work when book filter name equals to book name. It certainly is not what it meant to be. ".ExcludeProperties" accepts an array of expressions to allow excluding multiple poperties for automatic filtering condition generation in one call.
There there be any questions or suggestions regarding the library, please send an email to keeper013@gmail.com for inquiry. When submitting bugs, it's preferred to submit a C# code file with a unit test to easily reproduce the bug.