Filters

Use Where(...) for AND filters and OrWhere(...) for OR filters. Typed builders accept member selectors or CLR property-name strings.

var users = db.SelectFrom<User>()
    .Where(u => u.Id, Op.Eq, 1)
    .Where(u => u.Name, Op.Like, "A%")
    .OrWhere(u => u.Email, Op.IsNotNull)
    .Query();

Common operators include equality, comparisons, Like, In, and null checks:

.Where(u => u.Id, Op.In, new[] { 1, 2, 3 })
.Where(u => u.DeletedAt, Op.IsNull)
.Where(u => u.Name, Op.IsNotNull)

Op.Eq with null renders IS NULL, and Op.NotEq with null renders IS NOT NULL. Prefer Op.IsNull and Op.IsNotNull when no value is needed.

IN Subqueries

Use WhereIn(...), OrWhereIn(...), WhereNotIn(...), and OrWhereNotIn(...) when the IN list comes from another single-column Db4Net SELECT query.

var users = db.SelectFrom<User>()
    .WhereIn(
        u => u.Id,
        db.SelectFrom<Order>(o => o.UserId)
            .Where(o => o.Amount, Op.Gt, 100m))
    .Query();

The subquery must select exactly one column. Db4Net renders the subquery as SQL and keeps one shared parameter sequence across the outer query and nested query.

Grouped Filters

Use WhereGroup(...) and OrWhereGroup(...) when mixed AND and OR filters need explicit parentheses.

var users = db.SelectFrom<User>()
    .WhereGroup(group => group
        .Where(u => u.Id, Op.Eq, 1)
        .OrWhere(u => u.Name, Op.Eq, "Alice"))
    .Where(u => u.Id, Op.Gt, 0)
    .Query();

This renders grouped SQL like:

WHERE ([Id] = @p0 OR [Name] = @p1) AND [Id] > @p2

WARNING

Plain Where(...) and OrWhere(...) chains follow SQL operator precedence. They do not add parentheses automatically.