Searching on String Fields

Marten supports a subset of the common sub/string searches:

public void string_fields(IDocumentSession session)
{
    session.Query<Target>().Where(x => x.String.StartsWith("A"));
    session.Query<Target>().Where(x => x.String.EndsWith("Suffix"));

    session.Query<Target>().Where(x => x.String.Contains("something"));
    session.Query<Target>().Where(x => x.String.Equals("The same thing"));
}

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Marten also supports case insensitive substring searches:

public void case_insensitive_string_fields(IDocumentSession session)
{
    session.Query<Target>().Where(x => x.String.StartsWith("A", StringComparison.OrdinalIgnoreCase));
    session.Query<Target>().Where(x => x.String.EndsWith("SuFfiX", StringComparison.OrdinalIgnoreCase));

    // using Marten.Util
    session.Query<Target>().Where(x => x.String.Contains("soMeThiNg", StringComparison.OrdinalIgnoreCase));

    session.Query<Target>().Where(x => x.String.Equals("ThE SaMe ThInG", StringComparison.OrdinalIgnoreCase));

}

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A shorthand for case-insensitive string matching is provided through EqualsIgnoreCase (string extension method in JasperFx.Core):

(await query.Query<User>().SingleAsync(x => x.UserName.EqualsIgnoreCase("abc"))).Id.ShouldBe(user1.Id);
(await query.Query<User>().SingleAsync(x => x.UserName.EqualsIgnoreCase("aBc"))).Id.ShouldBe(user1.Id);

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Marten translates EqualsIgnoreCase to a PostgreSQL case-insensitive pattern-match (~~*, equivalent to ILIKE) rather than a .NET culture-aware comparison.

Regular Expressions 9.15

Regex.IsMatch() translates to the PostgreSQL regex match operator (~, or ~* for RegexOptions.IgnoreCase — the only supported option) on top-level members, and to a jsonpath like_regex predicate inside collection filters:

// WHERE d.data ->> 'UserName' ~ :pattern
session.Query<User>().Where(x => Regex.IsMatch(x.UserName, "^[a-z]+-\\d+$"));

// jsonb_path_exists(d.data, '$.Lines[*] ? (@.ItemName like_regex "...")')
session.Query<Order>().Where(x => x.Lines.Any(l => Regex.IsMatch(l.ItemName, "^item-1\\d$")));

Two caveats: PostgreSQL regular expressions are POSIX-flavored (like_regex is the SQL/JSON XQuery subset), so exotic .NET-specific constructs may behave differently. And inside collection filters the pattern is embedded in the SQL, so a compiled query cannot re-bind it between executions — Marten fails loudly if a compiled query member feeds such a pattern. Top-level Regex.IsMatch() stays fully parameterized and works in compiled queries.