Table of Contents

Projections

Return a column subset as a DTO instead of materializing the full entity. Useful when you need only a few columns from a wide table — no wasted bandwidth, no wasted allocation.

You write

Projections are supported by InquirySelectAll and InquirySelectAllByField, including their ordered and offset-paged forms. InquirySelectAllByPredicate, key lookups, keyset pages, and eager methods require the store entity. The predicate/projection restriction is intentional for 1.0; use a field equality filter or explicit parameterized SQL when returning a DTO. See Choosing a select declaration for the capability table and accepted API decision.

Declare a projection type with [InquiryProjection(typeof(SourceEntity))]. Only properties marked [InquiryColumn] are included; they map to columns on the source entity by name.

using Inquiry.Entities;

[InquiryProjection(typeof(Product))]
public sealed class ProductSummary
{
    [InquiryColumn] public int? ProductID { get; set; }
    [InquiryColumn] public string ProductName { get; set; } = "";
    [InquiryColumn] public decimal? UnitPrice { get; set; }
}

public partial class ProductStore : InquiryStore<Product>
{
    // Returns ProductSummary, not Product — the generator routes through the projection.
    [InquirySelectAll]
    public partial Task<IReadOnlyList<ProductSummary>> SelectSummariesAsync(CancellationToken ct = default);
}

What the generator emits

A separate materializer for ProductSummary and SQL that selects only the projected columns:

private const string _sqlSelectSummaries =
    "SELECT \"ProductID\", \"ProductName\", \"UnitPrice\" FROM \"Products\"";

Soft-delete entities

A projection over a soft-delete entity composes the active-row filter into the projected SELECT, even though the projected column subset doesn't include the soft-delete indicator:

private const string _sqlProj_SelectSummaries =
    "SELECT \"ProductID\", \"ProductName\", \"UnitPrice\" FROM \"Products\" WHERE \"IsDeleted\" = 0";

So a projection hides soft-deleted rows exactly like a full-entity select. Add IncludeDeleted = true to the query method to opt out and project deleted rows too.

See also

  • CRUD — full-entity selects.
  • Ad-hoc DTOs — result shapes that aren't a column subset of one entity (joins, GROUP BY reports), mapped from hand-written SQL.
  • Aggregates — return a single scalar.
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