We study the fundamental problem of learning an unknown object from data using a prescribed model class. We introduce a unified framework that accommodates objects in arbitrary Hilbert spaces, general (possibly vector-valued) random linear measurements and general types of nonlinear models. We establish novel learning guarantees for this framework that explicitly relate the required amount of data to structural properties of the model class, yielding near-optimal generalization bounds. A central concept we introduce is the variation of a model class relative to a distribution of sampling operators, which quantifies how the model interacts with the measurement process. Combined with entropy integrals that capture the model's complexity, this forms the foundation of our guarantees. Our framework is sufficiently general to recover and unify various well-known problems, such as matrix sketching, compressed sensing with isotropic measurements and compressed sensing with generative models. In each case, existing results arise as direct corollaries of our theory. For compressed sensing with generative models, we also derive the first guarantees for arbitrary Lipschitz generative maps combined with general linear measurements. Overall, our work provides a unified perspective on learning from general data and introduces novel theoretical guarantees that consolidate, sharpen and extend existing results.