Meziantou.Framework

Getting started

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Install the package

Add the Meziantou.Framework.SimpleQueryLanguage package to a project:

dotnet package add Meziantou.Framework.SimpleQueryLanguage

The examples of this documentation omit the using directives: they need using Meziantou.Framework.SimpleQueryLanguage;.

Filter a list

The examples search issues of this type:

internal sealed record Issue(string Title, string Author, bool IsOpen, int Comments, DateTime CreatedAt);

Create a QueryBuilder<Issue>, register what each key means, and build the query the user typed:

var queryBuilder = new QueryBuilder<Issue>();
queryBuilder.AddHandler("author", (issue, value) => issue.Author.Equals(value, StringComparison.OrdinalIgnoreCase));
queryBuilder.AddHandler("is", "open", issue => issue.IsOpen);
queryBuilder.AddHandler("is", "closed", issue => !issue.IsOpen);
queryBuilder.AddRangeHandler<int>("comments", (issue, range) => range.IsInRange(issue.Comments));
queryBuilder.SetTextFilterHandler((issue, text) => issue.Title.Contains(text, StringComparison.OrdinalIgnoreCase));

var issues = new[]
{
    new Issue("Crash on startup", "alice", IsOpen: true, Comments: 5, new DateTime(2026, 1, 10)),
    new Issue("Crash when saving", "bob", IsOpen: true, Comments: 0, new DateTime(2026, 2, 3)),
    new Issue("Typo in the readme", "alice", IsOpen: false, Comments: 1, new DateTime(2026, 3, 15)),
};

var query = queryBuilder.Build("is:open author:alice crash");
Assert.Equal(["Crash on startup"], issues.Where(query.Evaluate).Select(issue => issue.Title));
  • author:alice calls the author handler with alice.
  • is:open matches the handler registered for the value open of the key is.
  • comments is a range handler, so it also accepts comments>=2 or comments:1..5.
  • crash has no key: it is free text, passed to the text filter.
  • Terms separated by spaces must all match.

Build parses the query once. Keep the Query<Issue> and call Evaluate for each object.

Filter a database query

To filter an Entity Framework Core DbSet, use ExpressionQueryBuilder<T>: its handlers are expressions that the database can run. See Database queries.

Next steps