How to dynamically generate OR comparisons with LINQ?

Question

I have a query where I should find certain values comparing whether a column is equal to a value X.

X is an array that can have 1 to 4 values.

How can I in mine query with LINQ dynamically assemble these OR?

Below follows as is my code:

public List<Meta> ListaMetasDeCategorias(List<CategoriaMetaOrgao> ListaCategoriaMetaOrgao, int orgaoId, int temporadaId)
{
    List<int> arrayIdCategorias = new List<int>();
    foreach(CategoriaMetaOrgao categoriaMetaOrgao in ListaCategoriaMetaOrgao)
        arrayIdCategorias.Add(categoriaMetaOrgao.CategoriaMeta.categoriaMetaId);

    var q = from a in Repository.Context.Meta
            where a.Temporada.temporadaId == temporadaId
            && a.Orgao.orgaoId == orgaoId
            && (a.CategoriaMeta.categoriaMetaId == arrayIdCategorias[0] ||
            a.CategoriaMeta.categoriaMetaId == arrayIdCategorias[1] ||
            a.CategoriaMeta.categoriaMetaId == arrayIdCategorias[2] ||
            a.CategoriaMeta.categoriaMetaId == arrayIdCategorias[3])
            select a;

    return q.ToList();
}

In the section below, how can I make the comparison dynamically? Because the array will not always have the 4 values.

a.CategoriaMeta.categoriaMetaId == arrayIdCategorias[0] ||
a.CategoriaMeta.categoriaMetaId == arrayIdCategorias[1] ||
a.CategoriaMeta.categoriaMetaId == arrayIdCategorias[2] ||
a.CategoriaMeta.categoriaMetaId == arrayIdCategorias[3]

Answer 1

How you use version 1 of Entity Framework, also known as version 3.5, I see 2 possibilities to solve the problem.

1. One of them is to create an extension method for this.

public static IQueryable<TEntity> WhereIn<TEntity, TValue>
(
    this ObjectQuery<TEntity> query,
    Expression<Func<TEntity, TValue>> selector,
    IEnumerable<TValue> collection
)
{
    if (selector == null) throw new ArgumentNullException("selector");
    if (collection == null) throw new ArgumentNullException("collection");
    if (!collection.Any())
        return query.Where(t => false);

    ParameterExpression p = selector.Parameters.Single();

    IEnumerable<Expression> equals = collection.Select(value =>
       (Expression)Expression.Equal(selector.Body,
            Expression.Constant(value, typeof(TValue))));

    Expression body = equals.Aggregate((accumulate, equal) =>
        Expression.Or(accumulate, equal));

    return query.Where(Expression.Lambda<Func<TEntity, bool>>(body, p));
}

To use it:

public List<Meta> ListaMetasDeCategorias(List<CategoriaMetaOrgao> ListaCategoriaMetaOrgao, int orgaoId, int temporadaId)
{
    List<int> arrayIdCategorias = new List<int>();
    foreach(CategoriaMetaOrgao categoriaMetaOrgao in ListaCategoriaMetaOrgao)
        arrayIdCategorias.Add(categoriaMetaOrgao.CategoriaMeta.categoriaMetaId);

    var q = from a in Repository.Context.Meta
            where a.Temporada.temporadaId == temporadaId
            && a.Orgao.orgaoId == orgaoId
            select a;

    q.WhereIn(a => a.CategoriaMeta.categoriaMetaId, arrayIdCategorias);

    return q.ToList();
}

2. The other solution and that I do not recommend much is to transform your query to a list and then filter the Contains, the problem this way is that you are not making the filter in select, thus perhaps making your query heavier.

public List<Meta> ListaMetasDeCategorias(List<CategoriaMetaOrgao> ListaCategoriaMetaOrgao, int orgaoId, int temporadaId)
{
    List<int> arrayIdCategorias = new List<int>();
    foreach(CategoriaMetaOrgao categoriaMetaOrgao in ListaCategoriaMetaOrgao)
        arrayIdCategorias.Add(categoriaMetaOrgao.CategoriaMeta.categoriaMetaId);

    var q = from a in Repository.Context.Meta
            where a.Temporada.temporadaId == temporadaId
            && a.Orgao.orgaoId == orgaoId
            select a;

    var y = q.ToList().Where( a => arrayIdCategorias.Contains(a.CategoriaMeta.categoriaMetaId));


    return y;
}

Obs: If you used the Entity Framework 4 or higher, you could use the Contains, it picks up a list and checks if an element is in that list.

public List<Meta> ListaMetasDeCategorias(List<CategoriaMetaOrgao> ListaCategoriaMetaOrgao, int orgaoId, int temporadaId)
{
    List<int> arrayIdCategorias = new List<int>();
    foreach(CategoriaMetaOrgao categoriaMetaOrgao in ListaCategoriaMetaOrgao)
        arrayIdCategorias.Add(categoriaMetaOrgao.CategoriaMeta.categoriaMetaId);

    var q = from a in Repository.Context.Meta
            where a.Temporada.temporadaId == temporadaId
            && a.Orgao.orgaoId == orgaoId
            && arrayIdCategorias.Contains(a.CategoriaMeta.categoriaMetaId)
            select a;

    return q.ToList();
}

Answer 2

To List call for arrayIdCategorias has the method Any where it will sweep the array seeking to satisfy the condition.

In the case below, it sweeps the arrayIdCategorias looking for some value int equal to a.CategoriaMeta.categoriaMetaId.

In case he finds the Any returns true, if not false.

public List<Meta> ListaMetasDeCategorias(List<CategoriaMetaOrgao> ListaCategoriaMetaOrgao, int orgaoId, int temporadaId)
{
    List<int> arrayIdCategorias = new List<int>();
    foreach(CategoriaMetaOrgao categoriaMetaOrgao in ListaCategoriaMetaOrgao)
        arrayIdCategorias.Add(categoriaMetaOrgao.CategoriaMeta.categoriaMetaId);

    var q = from a in Repository.Context.Meta
        where a.Temporada.temporadaId == temporadaId
        && a.Orgao.orgaoId == orgaoId
        && arrayIdCategorias.Any(b=>b == a.CategoriaMeta.categoriaMetaId)
        select a;

    return q.ToList();
}