  We use three semi-analytic models (SAMs) of galaxy formation and evolution,
run on the same 1$h^{-1}$Gpc MultiDark Planck2 cosmological simulation, to
investigate the properties of [OII] emission line galaxies in the redshift
range $0.6<z<1.2$. We compare model predictions with different observational
data sets, including DEEP2--Firefly galaxies with absolute magnitudes. We
estimate the [OII] luminosity, L[OII], using simple relations derived both from
the models and observations and also using a public code. This code ideally
uses as input instantaneous star formation rates (SFRs), which are only
provided by one of the SAMs under consideration. We use this SAM to study the
feasibility of inferring galaxies' L[OII] for models that only provide average
SFRs. We find that the post-processing computation of L[OII] from average SFRs
is accurate for model galaxies with dust attenuated
L[OII]$\lesssim10^{42.2}$erg s$^{-1}$ ($<5\%$ discrepancy). We also explore how
to derive the [OII] luminosity from simple relations using global properties
usually output by SAMs. Besides the SFR, the model L[OII] is best correlated
with the observed-frame $u$ and $g$ broad-band magnitudes. These correlations
have coefficients (r-values) above 0.64 and a dispersion that varies with
L[OII]. We use these correlations and an observational one based on SFR and
metallicity to derive L[OII]. These relations result in [OII] luminosity
functions and halo occupation distributions with shapes that vary depending on
both the model and the method used. Nevertheless, for all the considered
models, the amplitude of the clustering at scales above 1$h^{-1}$Mpc remains
unchanged independently of the method used to derive L[OII].
