It was recently shown by van den Broeck at al. that the symmetric weighted first-order model counting problem (WFOMC) for sentences of two-variable logic FO 2 is in polynomial time, while it is #P1-complete for some FO 3 -sentences. We extend the result for FO 2 in two independent directions: to sentences of the form ϕ ∧ ∀x∃ =1 y ψ(x, y) with ϕ and ψ formulated in FO 2 and to sentences of the uniform one-dimensional fragment U1 of FO, a recently introduced extension of two-variable logic with the capacity to deal with relation symbols of all arities. We note that the former generalizes the extension of FO 2 with a functional relation symbol. We also identify a complete classification of first-order prefix classes according to whether WFOMC is in polynomial time or #P1-complete.The recent article [4] established the by now well-known result that the data complexity of WFOMC is in polynomial time for formulae of FO 2 , while [3] demonstrated that the three-variable fragment FO 3 contains formulae for which the problem is #P 1 -complete. We note that the non-symmetric variant of the problem is known to be #P-complete for some FO 2 -sentences [3].Weighted model counting problems have a range of well-known applications. For example, as pointed out in [3], WFOMC problems occur in a natural way in knowledge bases with soft constraints and are especially prominent in the area of Markov logic [6]. For a recent comprehensive survey on these matters, see [5]. From a mathematical perspective, WFOMC offers a neat and general approach to elementary enumerative combinatorics. To give a simple illustration of this, consider WFOMC(ϕ, n, w,w) for the two-variable logic sentence ϕ = ∀x∀y(Rxy → (Ryx ∧ x = y)) with w(R) =w(R) = 1. The sentence states that R encodes a simple undirected graph and thus WFOMC(ϕ, n, w,w) = 2 ( n 2 ) , the number of graphs of order n (with the set n of vertices). Thus WFOMC provides a logic-based way of classifying combinatorial problems. For instance, the result for FO 2 -properties from [4] shows that all these properties can be associated with tractable enumeration functions. For discussions of the links between weighted model counting, the spectrum problem and 0-1 laws, see [3].In the current paper, we extend the result of [4] for FO 2 in two independent directions. We first consider FO 2 with a functionality axiom, that is, sentences of type ϕ ∧ ∀x∃ =1 y ψ(x, y) with ϕ and ψ in FO 2 . This extension is motivated, inter alia, by certain description logics with functional roles [1]. The connection of WFOMC to enumerative combinatorics also provides an important part of the motivation. Indeed, while FO 2 is a reasonable formalism for specifying properties of relations, adding functionality axioms allows us to also express properties of functions, possibly combined with relations. For example, applying WFOMC to the sentence ∀x¬Rxx ∧ ∀x∃ =1 yRxy gives the number of functions that do not have a fixed point. While the extension of FO 2 with a functionality axiom might appear simple at first sight, showing th...